Drastic pH drop overnight with Mega Crop in DWC

regal8r · Mar 21, 2019

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 and change 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

regal8r · Mar 21, 2019

Forgot to mention I'm also using RO water.

PurplePotion · Mar 22, 2019

Used this nute before? Never heard of it. That’s a pretty big plant for 1 bucket. Wondering if the plant isn’t up taking so much that it’s just not enough water to stay stable. My limited advice would be to change nutes to something you know is stable and has worked in the past and/or increase your reservoir size. If I’m reading correctly, the 5gal bucket is your reservoir. If I’m not reading that correctly, how large is your res?

regal8r · Mar 22, 2019

PurplePotion said:
Used this nute before? Never heard of it. That’s a pretty big plant for 1 bucket. Wondering if the plant isn’t up taking so much that it’s just not enough water to stay stable. My limited advice would be to change nutes to something you know is stable and has worked in the past and/or increase your reservoir size. If I’m reading correctly, the 5gal bucket is your reservoir. If I’m not reading that correctly, how large is your res?

Mega Crop is made by Green Leaf Nutrients. This is my first time using it but it sounds like others that use it don't seem to have this problem, and even one has said that not even the raw pH of the powder isn't that low. It is possible that the res simply isn't big enough. It is 5 gal supporting a 2x2 SCROG. I may switch back to feeding with GH using the Lucas Method for a week and see what happens.

regal8r · Mar 22, 2019

PurplePotion said:
Used this nute before? Never heard of it. That’s a pretty big plant for 1 bucket. Wondering if the plant isn’t up taking so much that it’s just not enough water to stay stable. My limited advice would be to change nutes to something you know is stable and has worked in the past and/or increase your reservoir size. If I’m reading correctly, the 5gal bucket is your reservoir. If I’m not reading that correctly, how large is your res?

Also worth noting she's drinking about a gallon every 2 days.

f-e · Mar 22, 2019

A pH drop as the plant goes through 'the change' is normal. Some monitor for it, and after seeing it 3 days running, switch to flower food. It's a hormonal change in the plant, causing it to drop something in the tank. It's effect is much more prominent in a RO system as there is very little buffering. 2.2 though? jesus.

Hydro8 · Mar 22, 2019

I would first try to start at the top of the PH range 6.3 – 6.5 and then see how fast it drops.

My water has a the tendency to drop in PH. I start mine at 6.3 and over 7-14 days it will drift down to 5.7 then I know the nutes are getting spent and I put in fresh at 6.3.
From 5.5 down I can get fast drops.. especially when the plants are big. So I don't like to play in that range in my current conditions.

If you have no reservoir you are only dealing with 3 – 3.5 gallons of nutes that's not much for a plant in flower it might be burning through the nutes, if that is the case you will also want to start at the top of the PH range so it can take advantage of all the nutes as it drifts down.

regal8r · Mar 22, 2019

f-e said:
A pH drop as the plant goes through 'the change' is normal. Some monitor for it, and after seeing it 3 days running, switch to flower food. It's a hormonal change in the plant, causing it to drop something in the tank. It's effect is much more prominent in a RO system as there is very little buffering. 2.2 though? jesus.

So basically just keep monitoring and adjusting pH? And yeah, she's a hungry girl - I've heard it's the Cheese in her. Minor tip burn on select leaves but not widespread so I feel the higher EC is worth the very minor nute burn. I watch her very closely so I think we'll be fine. Thanks.

regal8r · Mar 22, 2019

Hydro8 said:
I would first try to start at the top of the PH range 6.3 – 6.5 and then see how fast it drops.

My water has a the tendency to drop in PH. I start mine at 6.3 and over 7-14 days it will drift down to 5.7 then I know the nutes are getting spent and I put in fresh at 6.3.
From 5.5 down I can get fast drops.. especially when the plants are big. So I don't like to play in that range in my current conditions.

If you have no reservoir you are only dealing with 3 – 3.5 gallons of nutes that's not much for a plant in flower it might be burning through the nutes, if that is the case you will also want to start at the top of the PH range so it can take advantage of all the nutes as it drifts down.

This is a good idea and may minimize the amount of drift over 24hrs since pH is on a logarithmic scale. I will definitely try this. You are correct that I have no aux res, just the 5gal DWC filled to 4ish gal. With it drinking about a gallon every 2 days, it makes sense that the drift would be so extreme. Thanks.

Douglas.Curtis · Mar 22, 2019

Burning through nutes causes pH to rise, not drop.

What's your res size?

What's your light wattage?

What are your solution temps?

What type of air pump(s) are you running? The standard used to be 3 watts of airpump power for every 10 gallons of nutrient solution.

Flower has more oxygen demands than veg, so a common issue is pH drop when entering flower.

Kudos on using r/o, any quality nutrient should have plenty of buffering capacity without depending on the infinite variable of "tap water". As you've found during veg, there were zero pH issues. This is not a pH buffering issue, I'm betting it's environmental.

brickweeder · Mar 22, 2019

Douglas.Curtis said:
Burning through nutes causes pH to rise, not drop.

Conversely, plants uptaking more water than nutes would mean the concentration of nutes increases in the bucket, which might be the cause of lower pH.

When the pH drops to less than 4, what is your EC?

If your bucket's EC at the low pH is higher than your starting EC, then the answer could be to lower your starting EC and try to reverse the drift direction.

But I like @Hydro8 's creative solution if you cant reverse the drift direction...start at the top of the pH range and take advantage of the drift downwards.

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regal8r · Mar 22, 2019

Douglas.Curtis said:
Burning through nutes causes pH to rise, not drop.

What's your res size?

What's your light wattage?

What are your solution temps?

What type of air pump(s) are you running? The standard used to be 3 watts of airpump power for every 10 gallons of nutrient solution.

Flower has more oxygen demands than veg, so a common issue is pH drop when entering flower.

Kudos on using r/o, any quality nutrient should have plenty of buffering capacity without depending on the infinite variable of "tap water". As you've found during veg, there were zero pH issues. This is not a pH buffering issue, I'm betting it's environmental.

5 gal res filled to 3.5-4 gal.

HLG 135w V2.

Res temps high 60's F.

Running a 60gal Tetra airpump with 4" airstone.

Do you suggest that I try and increase the res capacity somehow? Thanks.

regal8r · Mar 22, 2019

brickweeder said:
Conversely, plants uptaking more water than nutes would mean the concentration of nutes increases in the bucket, which might be the cause of lower pH.

When the pH drops to less than 4, what is your EC?

If your bucket's EC at the low pH is higher than your starting EC, then the answer could be to lower your starting EC and try to reverse the drift direction.

But I like @Hydro8's creative solution if you cant reverse the drift direction...start at the top of the pH range and take advantage of the drift downwards.

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I haven't been taking EC readings as religiously as pH but I want to say that it is going up which suggests that the plant is up taking water and not nutes. I will definitely pay more attention to daily change in EC though now. Thanks.

englishrick · Mar 23, 2019

try adding a touch of pk 13 14,,if this nute,,is anything like canna aqua it could well be dropping because it's meant to drop like canna aqua ,,it's litraly designed to do this when the plant demands pk

Douglas.Curtis · Mar 23, 2019

regal8r, it sounds like you have too much air for your reservoir size. The 5g bucket should be just fine, the goal is to have the swing take place over 7-10 days at the start of flower.

Can you do an experiment?

Check the pH of the res
Turn off the light and turn off the airpump for 15 minutes
Check the pH again

Is the pH higher or lower? If the pH has dropped, you have too much air going through your 4'ish gallons of solution.

I do know a few growers who start with a mild strength solution, pH'd to 6.0'ish. They do not top off daily, and the evaporation due to aeration over time causes the solution to concentrate over time. The pH is at around 5.4-3 when they eventually re-fill with whatever nute solution they top off with. I thought it was a lot of stress on the roots, being dried out for so long between re-fills. I knew both growers only briefly.

Englishrick, good point! I've never even thought of that being a 'feature' of nutrients.

In either case, reversing the process is indeed the solution as Hydro8 explained. At some point in the swing, they both allow cannabis free absorption of each element. .

Crowmax · Mar 23, 2019

brickweeder said:
Conversely, plants uptaking more water than nutes would mean the concentration of nutes increases in the bucket, which might be the cause of lower pH.

When the pH drops to less than 4, what is your EC?

If your bucket's EC at the low pH is higher than your starting EC, then the answer could be to lower your starting EC and try to reverse the drift direction.

But I like @Hydro8 's creative solution if you cant reverse the drift direction...start at the top of the pH range and take advantage of the drift downwards.

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^ that, sounds your feeding them too high.
Would be good to gradually lower it to 1.2 and see how it goes. You are lucky no damage seems to be done with so high EC that you have em.
Nice looking plants :tiphat:

LostTribe · Mar 24, 2019

f-e said:
A pH drop as the plant goes through 'the change' is normal. Some monitor for it, and after seeing it 3 days running, switch to flower food. It's a hormonal change in the plant, causing it to drop something in the tank. It's effect is much more prominent in a RO system as there is very little buffering. 2.2 though? jesus.

Where are you at in bloom? what day?

First thing I would do would be recalibrate my meters. Second, I would do would be drop your ec down.

LostTribe · Mar 24, 2019

regal8r said:
5 gal res filled to 3.5-4 gal.

HLG 135w V2.

Res temps high 60's F.

Running a 60gal Tetra airpump with 4" airstone.

Do you suggest that I try and increase the res capacity somehow? Thanks.

Thats your problem right there 3-4 gallons in a 5 gallon bucket and she's drinking a gallon a day. Thats the main problem when you try to run single unit DWC.

get a bigger container is an option.

Only way to fix it is add back multiple times per day. Your ec is rising and she's likely drinking more water than nutes. Drop your ec down and it may help.

regal8r · Mar 24, 2019

Crowmax said:
^ that, sounds your feeding them too high.
Would be good to gradually lower it to 1.2 and see how it goes. You are lucky no damage seems to be done with so high EC that you have em.
Nice looking plants

She's been fairly happy at this concentration at this. Could probably dial it back a little bit but right now I feel it's worth it since she looks pretty happy as long as I stay on the pH. I did start doing what another user suggested about pH'ing higher to give it more room to drift safely. Thanks for the kind words.

regal8r · Mar 24, 2019

LostTribe said:
Thats your problem right there 3-4 gallons in a 5 gallon bucket and she's drinking a gallon a day. Thats the main problem when you try to run single unit DWC.

Only way to fix it is add back multiple times per day. Your ec is rising and she's likely drinking more water than nutes. Drop your ec down and it may help.

Right now she's at about a gallon every 2 days. EC drift has seemed to level off when at about 2.0-2.2 EC since she's in the stretch right now but will likely dial it back a bit and give it a little extra bloom nutes once buds start packing on.

Drastic pH drop overnight with Mega Crop in DWC

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