DWC PH issues: Ph dropping like a rock - Please help

@firsttimeARE - Would you mind explaining the math you mentioned (550ppm minus 220ppm starting water)?

This is my first time doing a DWC so I am not sure why I need to be concerned with the starting PPM of my water when mixing up my nutrients. Isn't it the final PPM of your nutrient solution that you need to be concerned about?

John1961 said:

@firsttimeARE - Would you mind explaining the math you mentioned (550ppm minus 220ppm starting water)?

This is my first time doing a DWC so I am not sure why I need to be concerned with the starting PPM of my water when mixing up my nutrients. Isn't it the final PPM of your nutrient solution that you need to be concerned about?

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It is. But unless you know whats in that 220ppm,its best to negate it. So you are feeding 330ppm of actual nutrients

Good nutes are PH stable. If you were using GH and Lucas formula you wouldn't have to think about anything. I never go over 700 ppm any more and my 6 footers never have a yellow leaf. KISS

Good morning, folks. Another day, another PH drop.

Yesterday, I did another reservoir change. I waited four hours or so before taking the following readings:

Air temp: 67
Water temp: 65.3
Humidity: 32%
PH: 5.8
PPM: 550

Today, about 16 hours later, I took the following readings:

PH: 4.8
PPM: 560

Water level in my 5-gallon reservoir dropped by about a pint.

However, I think I have figured out the issue. There simply is no other explanation that I can think of.

When did this daily drop start happening? About a month or so ago, right about the time I turned on the gas furnace for the winter season. And where does my furnace sit? About 15 feet away from my grow cabinet.

So now I have to decide: Do I continue to use RO water, knowing that it sucks up CO2 like a sponge? I would have to continue to add 1.0 to 1.5 ML of PH-Up to the reservoir daily, not knowing how this might impact the plant. Or do I change to tap water, which would hopefully be more PH stable, not knowing what exactly is in the water to start with and having to deal with chlorine / chloramine?

Seriously, get your air temps up so the plant can transpire. Pointless trying to sort your ph right if your plant isn't feeding.

Looks like your using LEDs, you want air temp over 75.

you should think about doing a 24 hr flush with pH'd RO water like i suggested.

they still aren't eating. you still don't need ppms that high.

and the furnace has nothing to do with anything.

as corey said above, your air temps are still too low. with LED, you could go up to 80f but 75f is good enough.

OK, I managed to get my air temperature to stabilize at 70 degrees. I have the reservoir stable at 65 degrees. That's the best I'm gonna be able to do as far as temps go.

I completely understand how temps are important. However, I don't see how temps address my original problem of PH crashing each day.

Based on my own scouring of the internet, PH drops in Veg are usually caused by one of the following:

-- A bacterial / algae infection at the roots
-- Nutrient strength is too high
-- Somehow, I'm in a CO2-rich atmosphere and I'm pumping CO2 into the reservoir
Tomorrow, I'll do another reservoir change and this time I'm going to use tap water and hope for the best. I've tested it to 180 PPM and a PH of 8.5. If the PH in my reservoir continues to drop each day, then I simply have no choice but to keep using PH-Up every day to get my PH back in range.

John1961 said:

Nutrient strength is too high

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bingo.
your ppms went up 10 pts, not down.

John1961 said:

Somehow, I'm in a CO2-rich atmosphere and I'm pumping CO2 into the reservoir

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did you move the airpump out of the grow room like i suggested? if you have that much CO2 in your basement, you probably shouldn't be down there for long anyway.

a 24 hr flush with RO water is what i would do. then start back on even lighter nutes like 200ppm. you need to get them eating again. it takes 2 minutes to add more nutes once they start eating.

rkymtnman said:

bingo.
your ppms went up 10 pts, not down.

did you move the airpump out of the grow room like i suggested? if you have that much CO2 in your basement, you probably shouldn't be down there for long anyway.

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@rkymtnman - I really do appreciate you trying to help, but I'm having a hard time with your suggestion of dropping my nutrients even lower. The plant is already starving as it is. The plant is quite large, about 2.5 feet in circumference.

For the purpose of discussion, what if I eliminated nutrients altogether and do as you suggest, a complete reservoir change using only RO, PH'd water and then find my PH crashes again overnight? What would be the plan of attack?

And I have no way to get my air pump out of the basement / grow area. My basement is essentially one big, concrete room under the house. And as mentioned, I really don't know if CO2 is the problem; that's just what I've arrived at due to process of elimination.

John1961 said:

The plant is already starving as it is.

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that's your problem, you are nutrient locked. i've had it happen to me and what fixes it is a 24hr flush with RO water at 5.8pH. don't worry about your pH for the 24hrs, what you want to do is getting them eating again. after the 24hrs, give them light nutes as I said. they shoulld eat like crazy for the first couple of days. let's say you shoot for 200 ppm, i would almost bet it will be at 100 ppm within the first day. once they start eating again, let's revisit your pH issue.

and for the airpump, can you put it outside your grow closet/box and try it for a day or two? see if it helps at all. it might do nothing but it will eliminate it as a potential problem.

do a google search for nutrient lock-out in hydroponics. i would almost bet all the advice says to either use less nutes (we tried that) or plain water for 24hrs.

5 gallons of water.... 559ppm and 4.9pH.

Add 0.4g of KOH flakes.

Stop listening to these guys telling you to lower your ppm... Raise it to 1.3-1.8. RIU is obsessed with starving their plants.

Im having the same issue as you and im not really concerned with it, I am running at 900 ppm tds and i'm using tap water with 40ppm starting.

air temps 25c to 28c (night 18c)
humidity 34%
nutrient temp 17c to 18c (chilled)
nutrient 930ppm.

I would increase your ppm to maybe 700 to 800ppm, if your coming into flower your plants will be starving, don't concern yourself too much with ph drops as long as you haven't got any rot going on which will cause the ph to drop you should be fine just controlling the drop.
I will take mine to maybe 1200ppm/1300ppm dependant on the strain but just flipped 12/12 today so they will start drinking like crazy in a week or so. i have been feeding 800/900ppm since second week of veg with no issues.

Don't give up on it though its a great way to grow once you get used to it, I came from soil/coco growing but dwc kicks ass!
Things do happen very quickly in dwc and that includes the problems lol.
Im a year into rdwc now and my crops just keep getting better and bigger, 6 x plants in a tent with 2 x 600w hid lights and i managed to pull 9.79oz off one of my plants last grow.

Happy Growing Peace Out!

i would ask both members who recently suggested to raise your feed way up, why is my ppm's going up and not down? neither one addressed that issue.

good luck @John1961

Good morning, all! I have an interesting update this morning.

Yesterday, I experienced another unexplained drop in my reservoir PH. Yesterday morning, I added my usual 2ml of PH-Up to the reservoir to bring the PH back up to 6.1. But believe it or not, by 4:00 p.m., the PH had dropped to 4.3! I was livid to say the least.

So, at 4:00 p.m., I drained and refilled the reservoir again, this time using tap water. I mixed up my nutrient solution to 590 ppm and PH of 6.6. I left out Cal/Mag, assuming that the tap water would provide these elements. I did, however, add in 10ml of Hydroguard after I mixed everything up. Lights then went off at 7:00 p.m.

This morning at 8:00 a.m., I went to the basement to check on my lady and take some readings. The water level in the reservoir went down by about a quart overnight. The PH dropped slightly to 6.4 and my PPMs went down to 580 ppm. Air temperature is stable at 71 degrees and water temperature is steady at 67.4 degrees.

Based on today’s readings, this is my understanding. She is drinking and eating, albeit a small amount, which I guess is to be expected after the roller-coaster ride she’s been having. I went ahead and added 1.5ml of PH-Down to the reservoir to bring the PH down a little bit more. I also added some plain RO water to bring my water level back up.

So how do I proceed from here?

coreywebster said:

Seriously, get your air temps up so the plant can transpire. Pointless trying to sort your ph right if your plant isn't feeding.

Looks like your using LEDs, you want air temp over 75.

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His VPD is actually near ideal. At low humidity you want low temps.

John1961 said:

So how do I proceed from here?

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keep your pH in range.
if the ppm's keep dropping, that's good. if it drops 10 per day, you are very close to the ppm the plant wants.

steady as she goes...

I think you need to stop dumping the tubs so much and let things settle down, I had this issue to when I first started growing and tried dwc and found that I was being too aggressive on making everything perfect 100% of the time and did more harm than good. One thing , at least for me , I found was that ditching the traditional PH up and using silica in place of it dialed things in after a 4/5 day period of adjusting and they remained solid for the next 8-10 weeks of flower. Look into proteck silica, it's cheap and keeps the ph much more stable imho! The only things I used was dyna-gro foliage pro and bloom, proteck, a dash of mag pro and a little bit of floralicious at the end before straight water for the last two weeks. I never flushed my rez until the last two weeks so I could flush the plants and my ph and ppm always were on point. I just added back to the rez when needed tap water and the nutes with some silica and dash of hydrogen peroxide. Shit just worked out when I kept it simple. I fed my hempy buckets the same and they worked great to. These guys above talking about getting your temps right are on point..listen to them.

Although I agree with you that all of these res changes might have been a bit much, I thought it was a better option than continuing to use water that had so much PH-Up added to it already. I figured that starting over with fresh water would be less stressful.