Drastic pH drop overnight with Mega Crop in DWC

Hoping you guys can help me. I currently have Pineapple Chunk going in a 5gal DWC, day 8 of flower and using only Mega Crop 1 part at 2.2ish EC in RO water. I also change the solution every week religiously. Every day this week, I come home to check on my girl and find the res has a pH of <4. I'm having to add 1mL/gallon to get it back up to 5.6 pH. 24hrs later, it's back down to <4pH without fail. I use an Apera PH60 probe that I calibrate once a week and have no signs of root rot (normal smell and no sliminess) but just some staining. Here are some pics. TIA.

https://imgur.com/a/7hEBtTe

At this point, the only suggestion I would make would be to dump and reset your bucket with fresh solution and see.

GBAUTO said:

At this point, the only suggestion I would make would be to dump and reset your bucket with fresh solution and see.

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Yeah it's water change time tomorrow anyway. A user on ICMAG had pointed out that my res may be a bit small to support my 2x2 scrog which would inflate pH changes as the plant feeds bc of low res volume so I'm gonna go back to GH using the Lucas Method for a week and see if I still have crazy fluctuation. If so I will probably have to figure out a way to increase res volume to finish out this grow then move to a tote res or RDWC for in the future.

5 gal should be fine. I don't think it is res volume as much as something being off with your nutrients.

5BY5LEC said:

5 gal should be fine. I don't think it is res volume as much as something being off with your nutrients.

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That's what I thought too but who knows. She drinks about a gallon of water every 2 days. I guess we'll find out what happens when I switch back to GH tomorrow. Thanks!

No prob. Maybe the buffers in your Megacrop don't do RO well. At any rate your plants look nice so keep em that way.
Any input on your apera meter?I am thinking about getting the PC-60 for spot checks. Do you like it?

The Megacrop would probably work better with a lower EC and some cal mag in the water. If the ph still drops then I would add some silicon. When I use Megacrop with my tap water the ph rises too much. I always figured it would work better with RO water. Apparently not, so I would give the RO a little cal mag.

5BY5LEC said:

No prob. Maybe the buffers in your Megacrop don't do RO well. At any rate your plants look nice so keep em that way.
Any input on your apera meter?I am thinking about getting the PC-60 for spot checks. Do you like it?

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Definitely will. Apera is a real nice brand. I had to get mine replaced as soon as I bought it bc of a faulty screen and so they advanceadvance me a replacement with a shipping label for the faulty unit. The replaceable probes are also a nice feature.

70's natureboy said:

The Megacrop would probably work better with a lower EC and some cal mag in the water. If the ph still drops then I would add some silicon. When I use Megacrop with my tap water the ph rises too much. I always figured it would work better with RO water. Apparently not, so I would give the RO a little cal mag.

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Everyone I've seen says it doesn't need any extra CalMag but I have most of a brand new bottle so adding a couple mL/gal probably couldn't hurt.

I was having problems with my current grow in early veg. I was adding cal+mag+iron to my RO+DI to get 0.3 EC then rhino shin to get to 0.4 EC. Then I added megacrop until I got to 1.2 EC. pH swings like crazy... I kept adjusting pH to get to around 5.8. Plant got a little fried... got some spots... slow growth... overall unhealthy.

1. Solution Change: I poured RO+DI water into a 5 gal bucket... let it sit for 1 hour. Added 1 tsp per gallon of megacrop (about 1.2 EC). Let it sit for 1 hour. Nothing else added. Removed 5 gal from rez… replaced with new 5 gal solution. Did this 3 times over 3 days. I have about a 10 gal rez.

2. pH change: I thought I was having a mag deficiency, so I dropped to where it's more readily available. At 5.8, mag isn't very available. So I now let it swing from 5.2 to 5.8 instead of 5.5 to 6.1. It currently raises about .1 pH a day.

3. Temperature change: I increased the temps from mid 80*F to 90*F. I am running LED and I noticed the more heat that they can take, the better the growth rates. I run CO2, but only at 500ppm because it's a sealed grow and she will deplete it all otherwise. I have a chiller coming, as the rez temps have been slowly rising since my grow room is so hot. Was at 76*F last I checked... I want it below 70. (I actually just upped the temp to 95*F yesterday)

I don't know if any of that applies to you.

A drop in pH and water level usually indicates that the plant is drinking more water than nutes. Try lowering your nute levels. I run at 1.2 and I see no deficiency or burn.

Pic 1 is the day I started correcting things. Pic 2 is 8 days later (and 3 trims, and LST). Huge change. Ignore the condensation... I'm working that out (95*F + 80%RH = condensation on pretty much anything cool).

regal8r said:

Hoping you guys can help me.

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it did the same thing to me. would set it at 5.8 would go up to low 6's and then drop like a rock into the high 4/low 5's.

i shitcanned that bag of crap and went back to GH maxi series that is ph stable.

regal8r said:

Yeah it's water change time tomorrow anyway. A user on ICMAG had pointed out that my res may be a bit small to support my 2x2 scrog which would inflate pH changes as the plant feeds bc of low res volume so I'm gonna go back to GH using the Lucas Method for a week and see if I still have crazy fluctuation. If so I will probably have to figure out a way to increase res volume to finish out this grow then move to a tote res or RDWC for in the future.

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Just finished harvesting this chemdawg. Going to get a pound give or take and was in a 10 litre bucket! Would of been alot less maintenance if it was in a bigger bucket. Ph and ppm will be more stable in a larger res but if the plant is healthy and drinking your ph shouldnt swing that drastically. Just have to top up and adjust ppm/ph more often. Either time for a res change or id say itl be feed related. Did you add silica at all?

So silica. We're in week 3 of flower and I switched back to GH For now and pH is much more stable.

regal8r said:

So silica. We're in week 3 of flower and I switched back to GH For now and pH is much more stable.

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i had the same thing, the guy at megacrop tried to help but nothing they recommended fixed the pH dropping. a few other people here at RIU had the same thing happen so you aren't alone.

It sounds like your over reacting a bit, instead of lowering the megacrop. With Megacrop just ignore EC and ppm’s. Follow the directions on the back, or I do 2/3rd’s of the directed amount, and after initial ph adjustments (do water) to 5.8…after about 3 days..my ph is in the low 6’s…and on reservoir change day…it’s gone back up…but where I have found a problem is if I’m too busy to do a res. change, I am having to lower the ph like everyday/every other…and that usually gets me to clean the reservoir, and do it all over.
Just stay on top of things, and it seems MC thrives with clean water.
Maybe it had something to do with the organics in it, plus I have never used nutes that call for 4 GRAMS per GALLON!? So I’m thinking that there could be problems with using that much nutes so ya…I recommend 3 grams per gallon, as it’s seems to be a good feed, w.o too much. GL

nOizE16 said:

It sounds like your over reacting a bit, instead of lowering the megacrop. With Megacrop just ignore EC and ppm’s. Follow the directions on the back, or I do 2/3rd’s of the directed amount, and after initial ph adjustments (do water) to 5.8…after about 3 days..my ph is in the low 6’s…and on reservoir change day…it’s gone back up…but where I have found a problem is if I’m too busy to do a res. change, I am having to lower the ph like everyday/every other…and that usually gets me to clean the reservoir, and do it all over.
Just stay on top of things, and it seems MC thrives with clean water.
Maybe it had something to do with the organics in it, plus I have never used nutes that call for 4 GRAMS per GALLON!? So I’m thinking that there could be problems with using that much nutes so ya…I recommend 3 grams per gallon, as it’s seems to be a good feed, w.o too much. GL

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Megacrop has gone through two new versions since then at least, could explain the difference.

Rurumo said:

Megacrop has gone through two new versions since then at least, could explain the difference.

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I think they've added more carbonates in the new formulas which should mitigate some problems. I personally use potassium silicate as a buffer and I only see pH drop at the end of the day 10-11 when it's been used up.

I would personally never grow in hydro without adding potassium silicate. I see only benefits in hydro, you could argue about potency and to high potassium in late flower.

I've had friends passing out and go to the toilet after consuming my stuff, I don't need it to be any stronger than it already is.

Wastei said:

I think they've added more carbonates in the new formulas which should mitigate some problems. I personally use potassium silicate as a buffer and I only see pH drop at the end of the day 10-11 when it's been used up.

I would personally never grow in hydro without adding potassium silicate. I see only benefits in hydro, you could argue about potency and to high potassium in late flower.

I've had friends passing out and go to the toilet after consuming my stuff, I don't need it to be any stronger than it already is.

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I’m new to the Jack’s 321 line and there’s no silicon in it, as I’m sure you know. I’m getting some pretty good ph raise the first 2-3 days on a fresh tank, lots of ppm/EC going into the plants too. Do you think it’d be smart to run some silicon in my tank to help with the PH fluctuation or is it beneficial to let it happen.
What I mean is, when I mix a new tank the plants pull certain elements from it first, isn’t this what’s causing my ph raise in the first 2-3 days. After that I get the opposite, the ph drops, but that could be because the N,P,K and Mn are used up in the tank, so the ratio of ions changes. Do I want to add silicon to stabilize the PH and possibly slow down the absorption of the elements that are easy for the plant to absorb? Or am I better off letting that happen and just coping with the ph fluctuations?
I’m in hydro and my water is pretty nice at 55ppm (.11ec) so there‘s not a lot of carbonate in it to buffer the ph so I may be seeing the swings more than most people would. It’s the same issue as the OP had 2 years ago with Megacrop, water with no carbonates and none in the fert. I had real stable ph when I ran the gen hydro line, but it’s full of carbonates and bicarbonates to buffer the ph.

I’ve been reading some of Dr. bugbee’s reseach and he published this:

“The essential nutrients can be put into 3 categories based on how quickly they are
removed from solution. Group 1 elements are actively absorbed by roots and can be
removed from solution in a few hours. Group 2 elements have intermediate uptake rates
and are usually removed from solution slightly faster than water is removed. Group 3
elements are passively absorbed from solution and often accumulate in solution.

Table 1. Approximate uptake rates of the essential plant nutrients.

Group 1. Active uptake, fast removal
NO3, NH4, P, K, Mn

Group 2. Intermediate uptake
Mg, S, Fe, Zn, Cu, Mo, Cl

Group 3. Passive uptake, slow removal
Ca, B

One of the problems with individual ion monitoring and control is that the
concentration of the group 1 elements (N, P, K, Mn) must be kept low to prevent their toxic
accumulation in plant tissue”.

So the N,P,K,and Mn can be used up in a few hours according to him, would the addition of silicon slow this process? I do find the 321 to be a bit of a tip burner and it seems to happen after they drink up a bunch of ppm. Maybe silicon would help with that.

MustGro said:

321 to be a bit of a tip burner

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what does the EC come out to running it full strength?