DWC Rusting on top leaves - need help!

Hi guys ,

I’m running Mills nutrients - plants are particularly big as needed them to stabilise before flipping.
1.7-2 EC
PH 5.8-6
600 uMol Quantum Led
66 F Water temp
73 F Ambient Temp
50% RH
1200 PPM CO2

Some plant leaves are showing these rust spots on them, I supplemented low dose Athena Calmag but hasn’t solved 100% - any thoughts are very welcome!

Raise your ambient "light on" temp to at least 82f, with co2 I'd say 84-86 would be good. 73f for lights off is good. Lower your EC to about 1.2-1.4 for a little while. RH should be raised to about 60% under the conditions I just specified.

Edit: you using Epsom salts? What nutes are you using?

Mr. Mohaskey said:

Raise your ambient "light on" temp to at least 82f, with co2 I'd say 84-86 would be good. 73f for lights off is good. Lower your EC to about 1.2-1.4 for a little while. RH should be raised to about 60% under the conditions I just specified.

Edit: you using Epsom salts? What nutes are you using?

Click to expand...

Just reread the post and saw Mills nutes. I am not familiar with them so cannot comment on that.

Mr. Mohaskey said:

Just reread the post and saw Mills nutes. I am not familiar with them so cannot comment on that.

Click to expand...

thanks for your help .
i will raise the day temp (has been on my mind)
EC is currently at 2.2 will lower for a bit but doesn’t look like nutrient burn so much looks like calmag deficiency. i’m trying to grow 5 different strains so that’s not helping…

RH i’m worried about raising to 60% due to mildew mold which i’ve had before (am in costa rica)

LEDs are an entirely different animal when it comes to ambient temps. Temps need to be higher for the plant to transpire properly, then your humidity needs to be aligned with your stage of growth and temp. Once you get those dialed in your plant will start feeding properly. A lot of growers tend to think calmag issues are the culprit, when the actual factors are more likely Temps, humidity, overfeeding which leads to nutrient imbalances causing issues looking like calmag. Also Epsom salts are great for your plant.

Look VPD charts to help dial in your temp and humidity.

thanks a lot. attached is a VPD chart from one of my devices in the room. As for the epsom salts - what do you recommend for dosage ?

thanks . plants seem to be recovering well. day time temp is back to 78.

Here a chart i use to dial my Temps and humidity in.

Epsom salts i use 1.2 grams per gallon as part of my Jacks 321 feed program. Sometimes I add a little extra towards the end of flower. Don't know why, just do.

one of my plants still suffering , not sure why .

Fhawila said:

one of my plants still suffering , not sure why .

Click to expand...

You have had a nutrient imbalance for some time. Conditions in your grow have changed because 73° and 50% ≠ VPD of 1.9

VPD of 1.9 is tough on a plant. That's ~35% more water going through the plant than at 1.5 so there's lots of opportunity for a Ca deficit. I wouldn't try to correct that by adding more Ca since that won't get the Ca where it's needed. Jacks 3-2-1 uses Epsom to produce a balance set of chemicals. It's doubtful that adding Epsom to another line of ferts is a good strategy.

You're also at 1200PPM of CO2 but only 600µmol. I don't know that impact of that but, conceptually, the stomata are opening wide for that yummy CO2 but are "light starved" at only 600µmol. That might be causing adding to the higher-than-desirable rate of transpiration.

What's your leaf temperature offset?

My first move would be to get VPD down to 1.5, making sure I'm using the correct leaf temperature offset.

Second would be to increase light levels. 600 is conventional wisdom for veg but, especially since you're running CO2, you should be able to almost double your crop at higher light levels. Increasing PPFD to 1200 would add another ~50%. CO2 at 1200 gives ~30% boost. It's too late in the cycle for this grow but something to keep in mind for future grows.

Delps8 said:

You have had a nutrient imbalance for some time. Conditions in your grow have changed because 73° and 50% ≠ VPD of 1.9

VPD of 1.9 is tough on a plant. That's ~35% more water going through the plant than at 1.5 so there's lots of opportunity for a Ca deficit. I wouldn't try to correct that by adding more Ca since that won't get the Ca where it's needed. Jacks 3-2-1 uses Epsom to produce a balance set of chemicals. It's doubtful that adding Epsom to another line of ferts is a good strategy.

You're also at 1200PPM of CO2 but only 600µmol. I don't know that impact of that but, conceptually, the stomata are opening wide for that yummy CO2 but are "light starved" at only 600µmol. That might be causing adding to the higher-than-desirable rate of transpiration.

What's your leaf temperature offset?

My first move would be to get VPD down to 1.5, making sure I'm using the correct leaf temperature offset.

Second would be to increase light levels. 600 is conventional wisdom for veg but, especially since you're running CO2, you should be able to almost double your crop at higher light levels. Increasing PPFD to 1200 would add another ~50%. CO2 at 1200 gives ~30% boost. It's too late in the cycle for this grow but something to keep in mind for future grows.

Click to expand...

thank you for your detailed reply. I will check my leaf temperature offset tomorrow am. One issue is I have 5 different strains between two DWC systems so probably causing some nutrient issues. I have noticed that the EC goes up over time in the water so I assumed the plants were drinking more water than nutrients , so increasing light makes sense.

Below are some attachments of my avg temp humidity and VPD. maybe my humidifier swings the humidity too much during the day.

much appreciated

Fhawila said:

thank you for your detailed reply. I will check my leaf temperature offset tomorrow am. One issue is I have 5 different strains between two DWC systems so probably causing some nutrient issues.

Click to expand...

Different strains may have slightly different requirements but they're all cannabis so a standard nutrient mix should cover what the plants need. Part of what you're seeing is the change in VPD.

Fhawila said:

I have noticed that the EC goes up over time in the water so I assumed the plants were drinking more water than nutrients , so increasing light makes sense.

Click to expand...

If EC is rising, I'd add back a bit of RO.

Re. light levels - increased light will tend to increase growth and, therefore, nutrient demand. With the setup that you've got, you could be churning out some monstrous yields as long as your plants were getting the light they need.

Cannabis plants mature their ability to process light at about week 5. Is there a particular reason why you're at 600µmol?

Fhawila said:

Below are some attachments of my avg temp humidity and VPD. maybe my humidifier swings the humidity too much during the day.

much appreciated

Click to expand...

VPD is ranging quite a bit but RH is within a fairly narrow range. Temps, on the other hand, spike and then drop sharply later in the day. At 24, you're way down in terms of photosynthesis.

This is one of the graphics from the Chandra paper (attached). At 23° and 600µmol, your rate of photosynthesis is about 13µmol. If you can get that to 30° and 1000µmol, you will get about a 50% increase in photosynthesis.

Delps8 said:

Different strains may have slightly different requirements but they're all cannabis so a standard nutrient mix should cover what the plants need. Part of what you're seeing is the change in VPD.


If EC is rising, I'd add back a bit of RO.

Re. light levels - increased light will tend to increase growth and, therefore, nutrient demand. With the setup that you've got, you could be churning out some monstrous yields as long as your plants were getting the light they need.

Cannabis plants mature their ability to process light at about week 5. Is there a particular reason why you're at 600µmol?


VPD is ranging quite a bit but RH is within a fairly narrow range. Temps, on the other hand, spike and then drop sharply later in the day. At 24, you're way down in terms of photosynthesis.

This is one of the graphics from the Chandra paper (attached). At 23° and 600µmol, your rate of photosynthesis is about 13µmol. If you can get that to 30° and 1000µmol, you will get about a 50% increase in photosynthesis.
View attachment 5468815

Click to expand...

legendary info. thank you.

no reason as to why i have it at 600umol other than following a chart but forgetting to increase throughout flower.
Note i also have two quantum LEDs beneath the plants facing upwards (see photo below it’s from a few weeks ago - now i have some good buds beneath )

as for temperature - i had the temperature too low in general until a couple of weeks ago - since then i have been manually turning down the AC from 25c to 22c at night .

i think there’s about two weeks left of flower , is it worth turning light intensity up for the last two weeks?

thank you.

Fhawila said:

legendary info. thank you.

Click to expand...

I commend you for reading through it!

I hope you find it helpful. There's a lot there and I realize that I can come across with a pretty strong tone.

Fhawila said:

no reason as to why i have it at 600umol other than following a chart but forgetting to increase throughout flower.

Click to expand...

The worst culprit is the dreck at growlightmeter.com but most cannabis sites use the "legacy light levels", as I refer to them. No doubt, many growers have grown a lot of cannabis at 300, 300-600, and 600+ but those PPFD's are from the days of CMH and HPS. Technology has moved on and there's very little reason to limit a grow like that. Not that I have an opinion, of course!

Fhawila said:

Note i also have two quantum LEDs beneath the plants facing upwards (see photo below it’s from a few weeks ago - now i have some good buds beneath )

Click to expand...

that jumped right out at me. Great stuff!

My take - get 1kµmol on the canopy first then add supplemental underneath. Spectrum shapes plants but overall, more photons (preferably red) are the name of the game.

Fhawila said:

as for temperature - i had the temperature too low in general until a couple of weeks ago - since then i have been manually turning down the AC from 25c to 22c at night .

Click to expand...

Daytime temps are the big driver for growth. Higher temps allow the canopy to get larger sooner in the grow. The more space the grow occupies, the more photons it can capture. Cooler temps will tend to result in more buds, smaller buds and a lower "harvest index" which is the ratio of flower to above ground mass.

A lot of growers drop temps at night in search of improved quality but the research I'm reading doesn't support that. I'm churning through the PhD these of Mitch Westmoreland (Dr Mitch as of 8/24) who studied under Bruce Bugbee. Bugbee is a big wheel in the cannabis research world (head of Crop Physiology at Utah State University) and has a lot of good videos, full length and shorts, on YouTube.

Fhawila said:

i think there’s about two weeks left of flower , is it worth turning light intensity up for the last two weeks?

Click to expand...

As long as you can keep temps of the buds <78°, I'd give them more light. In one Bugbee video he's asked about 48 hours of darkness and his comment is that cannabinoids are being produced up until the moment of harvest so turning off the lights will immediately reduce photosynthesis and that will have a direct impact on cannabinoid production.
I leave mine on and use them when I'm cutting the plant down.

Fhawila said:

thank you.

Click to expand...

You're very welcome.

Delps8 said:

I commend you for reading through it!

I hope you find it helpful. There's a lot there and I realize that I can come across with a pretty strong tone.


The worst culprit is the dreck at growlightmeter.com but most cannabis sites use the "legacy light levels", as I refer to them. No doubt, many growers have grown a lot of cannabis at 300, 300-600, and 600+ but those PPFD's are from the days of CMH and HPS. Technology has moved on and there's very little reason to limit a grow like that. Not that I have an opinion, of course!


that jumped right out at me. Great stuff!

My take - get 1kµmol on the canopy first then add supplemental underneath. Spectrum shapes plants but overall, more photons (preferably red) are the name of the game.


Daytime temps are the big driver for growth. Higher temps allow the canopy to get larger sooner in the grow. The more space the grow occupies, the more photons it can capture. Cooler temps will tend to result in more buds, smaller buds and a lower "harvest index" which is the ratio of flower to above ground mass.

A lot of growers drop temps at night in search of improved quality but the research I'm reading doesn't support that. I'm churning through the PhD these of Mitch Westmoreland (Dr Mitch as of 8/24) who studied under Bruce Bugbee. Bugbee is a big wheel in the cannabis research world (head of Crop Physiology at Utah State University) and has a lot of good videos, full length and shorts, on YouTube.


As long as you can keep temps of the buds <78°, I'd give them more light. In one Bugbee video he's asked about 48 hours of darkness and his comment is that cannabinoids are being produced up until the moment of harvest so turning off the lights will immediately reduce photosynthesis and that will have a direct impact on cannabinoid production.
I leave mine on and use them when I'm cutting the plant down.


You're very welcome.

Click to expand...

if you had met my dad you would know a strong tone!!!

your help is like the hand of god . i have been growing for 5 years and always struggled to get the mega yields i have seen elsewhere. Max i have gotten is around 170g per plant.

I have hiked the ambient temps to 29 celcius ( i will measure the temps of the buds to make sure they don’t exceed 25 celcius - correct?)

max i can get out of my quantum lights is 750umol/m2 they are around 20 inches from my buds) should i lower to around 14 to get the 1000umol ?

Fhawila said:

if you had met my dad you would know a strong tone!!!

Click to expand...

Fhawila said:

your help is like the hand of god . i have been growing for 5 years and always struggled to get the mega yields i have seen elsewhere. Max i have gotten is around 170g per plant.

Click to expand...

Well, you haven't had to "back up the truck" during harvest yet but going back to basics is a good start.

First issue is decent genetics but that's easy to find. Even with the hated ILGM, I've had excellent results.

Grow environment



A lot of soil growers run into watering issues but, if that's nailed down, it should be smooth sailing.
Nutrients - same 18 chemicals no matter what pretty picture is on the label. I use a dry fert that comes in 25 pound bags, same formula from drop to chop.
CO2 - not an issue but put fans in the tent to ensure that you have air flow (leaves should rustle). That makes sure that there's a constant supply of CO2 which plants use for photosynthesis to make food.
Temperature and RH — 80-85 in veg and 70'ish RH. Once the canopy is built out, about week two of flower, temps of the colas should be <=78° to preserve cannabanoids.
I use VPD because it's easier. It seems that VPD doesn't click for a lot of growers but I think that's because they're getting the wrong info. That happens.
VPD >1.5 in flower is hard on a plant but, if it happens, drop EC and water more (soil) to avoid imbalances.
Light - ChatGPT and I disagree on this so I'm changing my processes to see if Chat is correct. My belief is that the ability for cannabis to process light matures at about week 5. That's based on about half a dozen grows and it fits the timeline of the veg vs flower stages. the purpose of veg is to prepare the plant for the flower stage. The plant creates the physical structures needed for that and it matures the processes that are needed, one of those being photosynthesis. My observation is that I can get to 1kµmol by about week 5 and, lo and behold, we flip to flower soon after that.
ChatGPT tells me that cannabis gets there at the 4 week mark. The only thing that I'm not doing that's not "optimal", best I can tell, is that I'm going light on ferts. I run at about EC 0.8 in early veg and then bump to EC 1 or so. ChatGPT suggested I bump EC so I'll give it a try for my next grow.
Autopotamus (the grower on You Tube) uses a much higher EC, doesn't have any nute preference. Check the video at this URL:


His comments at 46:00
"As long as you give them as much light as they possibly can take, they will grow huge. They don't need darkness."

He's notorious for getting "over a pound from his autos" and one plant came in at 26 oz. A pound per plant is not surprising but 26oz is quite something.

His trick? he maxes out his light (he doesn't use a PAR meter any more) and he runs his autos 24/0 from drop to chop.

Fhawila said:

I have hiked the ambient temps to 29 celcius ( i will measure the temps of the buds to make sure they don’t exceed 25 celcius - correct?)

Click to expand...

Yes. Growth rates plummet after the second week in flower. Westmoreland says that's when to get temps low enough to keep colas <=25°C.

From page 105 of Westmoreland's thesis "Lowering the temperature at the end of the lifecycle can also reduce temperature of developing fruit and flowers, which may improve quality (Wang and Camp, 2000)

and page 116 in the chapter where he grew plants at 18.5, 22.5, and 26.5 for the first four weeks and then changed the temps of some of them in flower. The goal was to see how the plans reacted to the different temperatures.



Depending on temperature, rapid growth stopped at various times depending on temperature and depending on the cultivar. Overall, though, it's better to make sure that the ambient temp is low enough that the buds are cooler rather than warmer.

Fhawila said:

max i can get out of my quantum lights is 750umol/m2 they are around 20 inches from my buds) should i lower to around 14 to get the 1000umol ?

Click to expand...

Ideally, you can get to the higher light level across the canopy but, like everything, there's a trade off. As hang height increases, the PPFD map gets more even but average PPFD drops.

What make and model light are you using? If I can find a PPFD map for it, I can give some idea about hang height. Another factor is that you're in a big space—what are the dimensions of the grow area and/or the canopy?

Delps8 said:

Well, you haven't had to "back up the truck" during harvest yet but going back to basics is a good start.

First issue is decent genetics but that's easy to find. Even with the hated ILGM, I've had excellent results.

Grow environment

View attachment 5468888

A lot of soil growers run into watering issues but, if that's nailed down, it should be smooth sailing.
Nutrients - same 18 chemicals no matter what pretty picture is on the label. I use a dry fert that comes in 25 pound bags, same formula from drop to chop.
CO2 - not an issue but put fans in the tent to ensure that you have air flow (leaves should rustle). That makes sure that there's a constant supply of CO2 which plants use for photosynthesis to make food.
Temperature and RH — 80-85 in veg and 70'ish RH. Once the canopy is built out, about week two of flower, temps of the colas should be <=78° to preserve cannabanoids.
I use VPD because it's easier. It seems that VPD doesn't click for a lot of growers but I think that's because they're getting the wrong info. That happens.
VPD >1.5 in flower is hard on a plant but, if it happens, drop EC and water more (soil) to avoid imbalances.
Light - ChatGPT and I disagree on this so I'm changing my processes to see if Chat is correct. My belief is that the ability for cannabis to process light matures at about week 5. That's based on about half a dozen grows and it fits the timeline of the veg vs flower stages. the purpose of veg is to prepare the plant for the flower stage. The plant creates the physical structures needed for that and it matures the processes that are needed, one of those being photosynthesis. My observation is that I can get to 1kµmol by about week 5 and, lo and behold, we flip to flower soon after that.
ChatGPT tells me that cannabis gets there at the 4 week mark. The only thing that I'm not doing that's not "optimal", best I can tell, is that I'm going light on ferts. I run at about EC 0.8 in early veg and then bump to EC 1 or so. ChatGPT suggested I bump EC so I'll give it a try for my next grow.
Autopotamus (the grower on You Tube) uses a much higher EC, doesn't have any nute preference. Check the video at this URL:

His comments at 46:00
"As long as you give them as much light as they possibly can take, they will grow huge. They don't need darkness."

He's notorious for getting "over a pound from his autos" and one plant came in at 26 oz. A pound per plant is not surprising but 26oz is quite something.

His trick? he maxes out his light (he doesn't use a PAR meter any more) and he runs his autos 24/0 from drop to chop.


Yes. Growth rates plummet after the second week in flower. Westmoreland says that's when to get temps low enough to keep colas <=25°C.

From page 105 of Westmoreland's thesis "Lowering the temperature at the end of the lifecycle can also reduce temperature of developing fruit and flowers, which may improve quality (Wang and Camp, 2000)

and page 116 in the chapter where he grew plants at 18.5, 22.5, and 26.5 for the first four weeks and then changed the temps of some of them in flower. The goal was to see how the plans reacted to the different temperatures.

View attachment 5468890
View attachment 5468889
Depending on temperature, rapid growth stopped at various times depending on temperature and depending on the cultivar. Overall, though, it's better to make sure that the ambient temp is low enough that the buds are cooler rather than warmer.


Ideally, you can get to the higher light level across the canopy but, like everything, there's a trade off. As hang height increases, the PPFD map gets more even but average PPFD drops.

What make and model light are you using? If I can find a PPFD map for it, I can give some idea about hang height. Another factor is that you're in a big space—what are the dimensions of the grow area and/or the canopy?

Click to expand...

thanks a lot noted on all the above .

i’m using these lights

grow area / canopy is 196cm x 110cm

i’m using two DWC systems 3 plants each. (but the chiller does move water from either side so essentially the same system)
trying to gauge the consumption of nutrients using EC. and it’s clear that they weren’t consuming what the Mills guide was suggesting , so in future i’m sure they will with the right amount of light. I will probably move the lights to within 15 inches of the buds to get closer to 900umol

thanks again

Fhawila said:

thanks a lot noted on all the above .

Click to expand...

Fhawila said:

i’m using these lights

Sunlike Full Spectrum Greenhouse Grow Lamps Quantum Board LM301H 240W V4

High quality Sunlike Full Spectrum Greenhouse Grow Lamps Quantum Board LM301H 240W V4 from China, China's leading Sunlike Full Spectrum LED Grow Light product, with strict quality control LM301H 240W Greenhouse Grow Lamps factories, producing high quality Sunlike Quantum Board LM301H 240W V4...

www.bavagreenled.com

Click to expand...

Hmm, the PPFD maps are "cattywampus" (great American expression for "mixed up"). The hang heights should be switched around and some of the numbers just don't look right.

At 12", PPFD is about 900µmol in the center area (the PPFD map on the bottom should be labeled 12") and when the light is raised to 24", it's a little under 50% of the PPFD. That makes sense. What doesn't make sense are the PPFD values around the perimeter—they're almost the same values at 24" as they are at 12".

Fhawila said:

grow area / canopy is 196cm x 110cm

Click to expand...

(77" x 43" or 6 ½' x 3 ½' )
["thinking out loud"]

You're well into flower and at the point where temperature of the buds takes priority over max PPFD. The plants are still processing light but they're not creating vegetation, they're bulking up and generating secondary metabolites so I would not reduce light levels.

If you can get more light on the canopy by lowering the lights, I think that's a sound tactic but, because it's so late in flower, I think we're well into past the point where there will be a significant change.

A grow that's averaged 950µmol over the course of the grow will yield about 4% more than a grow that's received 900µmol over the course of the grow. This grow is in the last two weeks± so adding extra light won't accomplish much and it's a definite "No" if it will increase canopy temp.

Recommendation for next grow is to get a lux meter. I've tested Photone and it's OK in my book as long as you are using a diffuser. When I tested it, it came out 16% high and after trading emails with the programmer (I've been/was a software engineer for 30+ years), I bought a PAR meter. If I were starting over, I'd go with a lux meter. They're a good way to get an idea of how much light is hitting the different parts of your grow and it would help you position your lights better (horizontally) as well as make it easier to adjust hang height and dimmer setting to get good light across the plant canopies.

Fhawila said:

i’m using two DWC systems 3 plants each. (but the chiller does move water from either side so essentially the same system)
trying to gauge the consumption of nutrients using EC. and it’s clear that they weren’t consuming what the Mills guide was suggesting , so in future i’m sure they will with the right amount of light. I will probably move the lights to within 15 inches of the buds to get closer to 900umol

thanks again

Click to expand...

That's a good sized grow and having two reservoirs adds a lot of stability to the system. I grow in a 2' x 4' tent but the res holds 28 gallons/105 liters so pH is very stable and EC falls very gradually.

"trying to gauge the consumption of nutrients using EC" - EC cannot tell you much. EC is helpful when mixing nutrients because, if you mix them correctly, you should have the EC that the manufacturer specifies. The reason that you can't tell what's in the res by using EC is that the chemicals in ferts are taken up at different rates. N, P, K, and Mg are taken up very quickly whereas Ca is taken up very slowly. And the chemicals have different impacts on EC. N, P, and K don't cause much of a drop EC whereas Ca does.

Hit YouTube and search for "Bugbee nutrients hydroponics Athena" and you'll get a series of "shorts". There's a handful of very helpful videos that are 5-8 minutes long. The big thing that I'm starting to understand is how the different processes are interdependent. The vids that Bugbee does will help put the pieces together.

I've attached a couple of documents on reservoir management. One is from Bugbee and it's got interesting info on what actually happens in the res and it also touches on the concept of "mass balance". In a YouTube short, Bugbee advocates adding back full strength nutrients.

The other is from CannaStats and the author discusses, among other things, the concept of adding back with RO and then replacing the res when you've added back a volume equal to the system volume.

I've used both approaches, adding back nutes and adding RO, and have had good results with both but adding back nutes is less work because you don't have to track the amount you've added back.

One item — your plants are very green, enough so that I'd suspect that they're getting too much N. It's not in toxicity range but they're strikingly green to my eye. I think you're at the high end of "High" range AKA "luxury consumption".

Key point for nutrients is that there's a misconception about "pushing nutes". "More nutes" will not make a plant grow faster. Once nutrients are in the sufficiency range, adding more might take the plant into toxicity. Nutrients are taken up by the plant in response to the demands of the plant.

Delps8 said:

Hmm, the PPFD maps are "cattywampus" (great American expression for "mixed up"). The hang heights should be switched around and some of the numbers just don't look right.

At 12", PPFD is about 900µmol in the center area (the PPFD map on the bottom should be labeled 12") and when the light is raised to 24", it's a little under 50% of the PPFD. That makes sense. What doesn't make sense are the PPFD values around the perimeter—they're almost the same values at 24" as they are at 12".


(77" x 43" or 6 ½' x 3 ½' )
["thinking out loud"]

You're well into flower and at the point where temperature of the buds takes priority over max PPFD. The plants are still processing light but they're not creating vegetation, they're bulking up and generating secondary metabolites so I would not reduce light levels.

If you can get more light on the canopy by lowering the lights, I think that's a sound tactic but, because it's so late in flower, I think we're well into past the point where there will be a significant change.

A grow that's averaged 950µmol over the course of the grow will yield about 4% more than a grow that's received 900µmol over the course of the grow. This grow is in the last two weeks± so adding extra light won't accomplish much and it's a definite "No" if it will increase canopy temp.

Recommendation for next grow is to get a lux meter. I've tested Photone and it's OK in my book as long as you are using a diffuser. When I tested it, it came out 16% high and after trading emails with the programmer (I've been/was a software engineer for 30+ years), I bought a PAR meter. If I were starting over, I'd go with a lux meter. They're a good way to get an idea of how much light is hitting the different parts of your grow and it would help you position your lights better (horizontally) as well as make it easier to adjust hang height and dimmer setting to get good light across the plant canopies.


That's a good sized grow and having two reservoirs adds a lot of stability to the system. I grow in a 2' x 4' tent but the res holds 28 gallons/105 liters so pH is very stable and EC falls very gradually.

"trying to gauge the consumption of nutrients using EC" - EC cannot tell you much. EC is helpful when mixing nutrients because, if you mix them correctly, you should have the EC that the manufacturer specifies. The reason that you can't tell what's in the res by using EC is that the chemicals in ferts are taken up at different rates. N, P, K, and Mg are taken up very quickly whereas Ca is taken up very slowly. And the chemicals have different impacts on EC. N, P, and K don't cause much of a drop EC whereas Ca does.

Hit YouTube and search for "Bugbee nutrients hydroponics Athena" and you'll get a series of "shorts". There's a handful of very helpful videos that are 5-8 minutes long. The big thing that I'm starting to understand is how the different processes are interdependent. The vids that Bugbee does will help put the pieces together.

I've attached a couple of documents on reservoir management. One is from Bugbee and it's got interesting info on what actually happens in the res and it also touches on the concept of "mass balance". In a YouTube short, Bugbee advocates adding back full strength nutrients.

The other is from CannaStats and the author discusses, among other things, the concept of adding back with RO and then replacing the res when you've added back a volume equal to the system volume.

I've used both approaches, adding back nutes and adding RO, and have had good results with both but adding back nutes is less work because you don't have to track the amount you've added back.

One item — your plants are very green, enough so that I'd suspect that they're getting too much N. It's not in toxicity range but they're strikingly green to my eye. I think you're at the high end of "High" range AKA "luxury consumption".

Key point for nutrients is that there's a misconception about "pushing nutes". "More nutes" will not make a plant grow faster. Once nutrients are in the sufficiency range, adding more might take the plant into toxicity. Nutrients are taken up by the plant in response to the demands of the plant.

View attachment 5468932

Click to expand...

thank you .

i was watching the podcast of that guy growing over 1lb from an auto flower. INSANE

he is using this light which i could get .

currently my buds were too hot around 28.5celcius so i have lowered the ambient temp to 25 again.

i think getting one of these lights is key to get the umol up without affecting temperature of bud sites too much.

next grow is the one !!