Ph Dropping From 5.8 To 3.9 Overnight! What Is Causing This?

[RFT]

95+% of ph problems are inadequate alkalinity. Aka carbonate, bicarbonate. That's what provides the stability. So many times people will say my ph is rising from say 5.6 to 7 in 12hrs. I will tell them to add a buffer like baking soda (sodium bicarbonate) cause most ppl have it (ideally avoid sodium). Any they are like my ph is rising why would I want to add something that going to increase it. The reason is because then it takes more acid to lower the ph so in the end you get a much more stable ph. Same goes for ph dropping quickly. You have more acid but little buffer and as the buffer is used up the ph drops fast.

I dont necessarily think I have a pH problem per se. I think the pH dropping is just a symptom of the actual issue. Why? Because my pH has no problem staying stable for the first 4 weeks of flower. It's only in the 4th/5th weeks do I see things take a dive for the worst.

My source well water is plenty alkaline. It's about 7.5 on it's own. Which means a fair amount of pH down is added to get things in the 5.6-6.0 range.

I dont think adding more stabilizer will fix the root issue, if my theory is correct and the root issue happens to be that a sudden feeding of P-K by the plants is removing the pH stabilizing they provide once they're eaten up (leaving an excess of pH down still left in the solution and thus the dive). Ultimately tho, I wont know if I just add pH stabilizing products so that my pH doesnt swing. My plants will still be left short on the P-K they obviously want more of.

I just flushed the tanks again. Going with a higher ratio of P-K. Let's see if that stabilizes the pH for the entire week or if it dives again a few days from now.

I've already lowered the EC enough to probably rule out EC burn as being the pH drop culprit. Im at 1.4 currently after this flush. If the EC level is right, we should see it drop day by day right? Assuming I got the NPK ratios finally on point.

 

[Aqua Man]

I dont necessarily think I have a pH problem per se. I think the pH dropping is just a symptom of the actual issue. Why? Because my pH has no problem staying stable for the first 4 weeks of flower. It's only in the 4th/5th weeks do I see things take a dive for the worst.

My source well water is plenty alkaline. It's about 7.5 on it's own. Which means a fair amount of pH down is added to get things in the 5.6-6.0 range.

I dont think adding more stabilizer will fix the root issue, if my theory is correct and the root issue happens to be that a sudden feeding of P-K by the plants is removing the pH stabilizing they provide once they're eaten up (leaving an excess of pH down still left in the solution and thus the dive). Ultimately tho, I wont know if I just add pH stabilizing products so that my pH doesnt swing. My plants will still be left short on the P-K they obviously want more of.

I just flushed the tanks again. Going with a higher ratio of P-K. Let's see if that stabilizes the pH for the entire week or if it dives again a few days from now.

I've already lowered the EC enough to probably rule out EC burn as being the pH drop culprit. Im at 1.4 currently after this flush. If the EC level is right, we should see it drop day by day right? Assuming I got the NPK ratios finally on point.

Fair enough. They don't use much P though. And just want to point out there is a big difference between alkalinity and ph. Although the do kinda work together. Nutrient ratios can have an impact but in those concentrations and a bigger volume system I can't see it being that pronounced. If you have a lot of bacteria or microbial life and poor aeration it could also affect it. I have a feeling it not one culprit but a number of small contributing factors.

 

[RFT]

Nutrient ratios can have an impact but in those concentrations and a bigger volume system I can't see it being that pronounced.

It all depends on the NPK ratios tho doesnt it? If I have a more even blend, and yet the plant doesnt want a lot of nitrogen in the 4th week, it's not going to eat much of it. So my EC will remain relatively stable. Meanwhile the available P & K will get gobbled up and then there wont be any left, when the plant probably wants more.

I dunno. Im just grasping at straws here.

But the theory is that if I get the ratios right, I'll see the overall EC drop because all the nutes are being eaten up at a relatively even amount. And thus there wont be an abundance of anything left over to leave a higher EC reading. The auto doser will see the lowered EC, and automatically top off the solution. And in turn add more nutes which will continue to keep the overall solution well pH buffered.

If you have a lot of bacteria or microbial life and poor aeration it could also affect it. I have a feeling it not one culprit but a number of small contributing factors.

Shouldnt be much bacteria or microbial since Im using that calcium hypochlorite to keep the algae at bay, of which it is doing a fine job at.

And you may very well be right, it could be a number of contributing factors.

The two leading causes (if one were to do a quick google search) is too high EC, of which I have addressed. And the other told to me by 2 separate nutrient techs is that whatever nute the plant is eating up is removing that particular nute's buffering capabilities from the solution. So add more of that nute and things will stabilize. This theory makes sense because of the plateau the plants have hit every 4th week as well.

Time & testing will tell the truth tho. So we'll see how this week goes.

 

[Aqua Man]

It all depends on the NPK ratios tho doesnt it? If I have a more even blend, and yet the plant doesnt want a lot of nitrogen in the 4th week, it's not going to eat much of it. So my EC will remain relatively stable. Meanwhile the available P & K will get gobbled up and then there wont be any left, when the plant probably wants more.

I dunno. Im just grasping at straws here.

But the theory is that if I get the ratios right, I'll see the overall EC drop because all the nutes are being eaten up at a relatively even amount. And thus there wont be an abundance of anything left over to leave a higher EC reading. The auto doser will see the lowered EC, and automatically top off the solution. And in turn add more nutes which will continue to keep the overall solution well pH buffered.



Shouldnt be much bacteria or microbial since Im using that calcium hypochlorite to keep the algae at bay, of which it is doing a fine job at.

And you may very well be right, it could be a number of contributing factors.

The two leading causes (if one were to do a quick google search) is too high EC, of which I have addressed. And the other told to me by 2 separate nutrient techs is that whatever nute the plant is eating up is removing that particular nute's buffering capabilities from the solution. So add more of that nute and things will stabilize. This theory makes sense because of the plateau the plants have hit every 4th week as well.

Time & testing will tell the truth tho. So we'll see how this week goes.

Most nutrients are passively taken up the plant doesn't have a whole lotta say... Thats why you get toxicity and deficiency issues and ratios are important. Otherwise you just throw in a hot ton of everything and let the plant decide. Rate of uptake and nutrient concentrations yes can impact your ph. Kinda why I feel it's a buffer and concentration issue. A lot of ppl think ph directly translates to alkalinity but that's not the case.

Have you tried increasing the aeration? The is a possibility gas exchange is no longer adequate for the system demands so you could be getting an increase in carbonic acid. Easy to test... Pull some water out of the tank and aerate the shit out of it for a couple hours then check the ph and see if it has risen

 

[RFT]

Most nutrients are passively taken up the plant doesn't have a whole lotta say... Thats why you get toxicity and deficiency issues and ratios are important. Otherwise you just throw in a hot ton of everything and let the plant decide. Rate of uptake and nutrient concentrations yes can impact your ph. Kinda why I feel it's a buffer and concentration issue. A lot of ppl think ph directly translates to alkalinity but that's not the case.

Have you tried increasing the aeration? The is a possibility gas exchange is no longer adequate for the system demands so you could be getting an increase in carbonic acid. Easy to test... Pull some water out of the tank and aerate the shit out of it for a couple hours then check the ph and see if it has risen

Checking the dissolved oxygen levels is on the agenda for sure. But it's low probability considering this is NFT and there is PLENTY of aeration points where the water surface plane is being broken. Be it the feed straws or the return manifold, or the chiller pump, or the auto doser return line.

I like your simple test tho. Worth trying.

 

[Aqua Man]

Checking the dissolved oxygen levels is on the agenda for sure. But it's low probability considering this is NFT and there is PLENTY of aeration points where the water surface plane is being broken. Be it the feed straws or the return manifold, or the chiller pump, or the auto doser return line.

I like your simple test tho. Worth trying.

I would agree highly unlikely but easy

 

[RFT]

I would agree highly unlikely but easy

For all the aeration points, one thing that has concerned me is the reservoir itself is sealed. So the air is a bit stale. The true aeration points are the feed straws per each gutter channel and the return manifold where the gutter channels spill into. Those are both open air points where the water surface plane is broken.

The return plumbing from the chillers and the auto doser, while both are huge 1" streams of water being recirculated back into the reservoir, it's not like they're hitting open air. They're breaking the surface of the water plane within a sealed up reservoir. So Im not sure how much actual aeration is occuring.

The original design of this NFT system called for a venturi line to be installed into the plumbing of the reservoir so that fresh air was sucked into the solution constantly. But since I had this auto dosing & chiller plumbing (something the original plans did not account for) then I thought they would serve the same aeration purpose. But I could have miscalculated by the simple fact that they are simply recirculating stale air. Unlikely but very well could be the culprit if DO is the root issue here.

I think a simple test to see if I can raise the pH (if it dips again) by getting better aeration would be to crack (or remove) the reservoir lid so that fresh air is easily available to the inside of the reservoir. Within a few hours your same experiment would show the pH rise back up.

 

[Aqua Man]

Ok just a thought here what nutrients are you using? So you have ammonium/ammonium in them or have you tested the source water for it?

 

[RFT]

Ok just a thought here what nutrients are you using? So you have ammonium/ammonium in them or have you tested the source water for it?

Still waiting source water test results.

Nutes are GH FloraDuo, Liquid Kool Bloom, Silica, Diamond Nectar.

Have tested plenty with two other nutrient lines. Same issue persisted. Ruling out the issue being a nutrient brand issue. But I can say that with the other brands, I was quite easily shorting the plants on P-K in those instances as well.

 

[Aqua Man]

For all the aeration points, one thing that has concerned me is the reservoir itself is sealed. So the air is a bit stale. The true aeration points are the feed straws per each gutter channel and the return manifold where the gutter channels spill into. Those are both open air points where the water surface plane is broken.

The return plumbing from the chillers and the auto doser, while both are huge 1" streams of water being recirculated back into the reservoir, it's not like they're hitting open air. They're breaking the surface of the water plane within a sealed up reservoir. So Im not sure how much actual aeration is occuring.

The original design of this NFT system called for a venturi line to be installed into the plumbing of the reservoir so that fresh air was sucked into the solution constantly. But since I had this auto dosing & chiller plumbing (something the original plans did not account for) then I thought they would serve the same aeration purpose. But I could have miscalculated by the simple fact that they are simply recirculating stale air. Unlikely but very well could be the culprit if DO is the root issue here.

I think a simple test to see if I can raise the pH (if it dips again) by getting better aeration would be to crack (or remove) the reservoir lid so that fresh air is easily available to the inside of the reservoir. Within a few hours your same experiment would show the pH rise back up.

Roots can release CO2 so it's unlikely this is happening but they could increase CO2 (carbonic acid) in the root zone and with no aeration that could affect ph but unlikely. Gases in water are independent so just because DO is high does not mean CO2 in the form of carbonic acid will be any higher or lower.

 

[RFT]

Roots can release CO2 so it's unlikely this is happening but they could increase CO2 (carbonic acid) in the root zone and with no aeration that could affect ph but unlikely. Gases in water are independent so just because DO is high does not mean CO2 in the form of carbonic acid will be any higher or lower.

I would think carbonic acid is very unlikely then. Simply because in NFT there is a LOT of exit points for the Co2 to escape the channels from.

 

[Aqua Man]

Not necessarily brand but source of nitrogen. Be it ammonium, nitrite or nitrate. When plants take up ammonium there is an extra process releasing more h+ ions and lowering the ph. This is why we should stay away from ammonium sources in hydro. It's possible in the water supply also. It makes sense as the plants get bigger and take up more nutrients this become a bigger issue

 

[Aqua Man]

Not necessarily brand but source of nitrogen. Be it ammonium, nitrite or nitrate. When plants take up ammonium there is an extra process releasing more h+ ions and lowering the ph. This is why we should stay away from ammonium sources in hydro. It's possible in the water supply also. It makes sense as the plants get bigger and take up more nutrients this become a bigger issue

If that the case a stronger buffer will be a temp fix until you find the source

 

[RFT]

This is why we should stay away from ammonium sources in hydro.

Being that this is General Hydroponics brand nutes, Im sure the product is designed specifically for hydro.

Either way, if indeed it was a nitrogen source issue, I would think this issue would show itself much earlier on especially when the nitrogen uptake is at it's highest.

It's possible in the water supply also.

Very much a possibility still. I eagerly await my water test results.

 

[bunkerking]

The flora series nutes shouldn't have a high % of ammonia. Humic acid though, great buffer.

Try a small batch without it and see if early stability goes out the window?

 

[Aqua Man]

I mean I have run into this also.. I just increase my buffer and never I'll effects but never a ph drop like this. I have some ammonia in my nutes. The first time it threw me but I was also over feeding. Once I dialed in my buffer in the next grows and cut my feed and pk back it's not an issue. So idk why it's sooo pronounced in this grow? I mean yes some CO2 from bigger roots but good aeration should make that nil. Also increased dark period means more h+ ions released during calvin cycle could equate to some, ammonium the plant releases more h+ ions to process. Higher ppm can be more acidic. Add these up and maybe but...

Something I need to dig more into is the ion exchange of other nutrients.

@cemchris might be able to shed some light on this.

 

[Aqua Man]

Ok come to think of it I know what might have fixed it for me. I also use denitrifying bacteria after that. And they break ammonia/ammonium down into nitrates...

Back to square 1

 

[RFT]

The flora series nutes shouldn't have a high % of ammonia. Humic acid though, great buffer.

Try a small batch without it and see if early stability goes out the window?

I’ve done entire grow cycles without the humics.

pH drop still occured mid/late cycle.

 

[RFT]

I mean I have run into this also.. I just increase my buffer and never I'll effects but never a ph drop like this. I have some ammonia in my nutes. The first time it threw me but I was also over feeding. Once I dialed in my buffer in the next grows and cut my feed and pk back it's not an issue. So idk why it's sooo pronounced in this grow? I mean yes some CO2 from bigger roots but good aeration should make that nil. Also increased dark period means more h+ ions released during calvin cycle could equate to some, ammonium the plant releases more h+ ions to process. Higher ppm can be more acidic. Add these up and maybe but...

Something I need to dig more into is the ion exchange of other nutrients.

@cemchris might be able to shed some light on this.

I’ve tried scaling back the nutes more & more. Im at 1.4 EC now. How much further must I lower my nutes?

Only thing I can say is that I’ve read that if EC is at right level, it should drop 0.1 per day because plants are feeding. If the EC is not dropping, their is likely lockout. Your thoughts?

 

[Aqua Man]

I’ve tried scaling back the nutes more & more. Im at 1.4 EC now. How much further must I lower my nutes?

Only thing I can say is that I’ve read that if EC is at right level, it should drop 0.1 per day because plants are feeding. If the EC is not dropping, their is likely lockout. Your thoughts?

I mean my ph drift is always slower in flower. I can't out my finger on it yet. But like I say I think it's a combination of the plants process and rapid growth. Root respiration, nutrient uptake and concentration, calvin cycle at it's longest and growth at it fastest I think adding these all up can explain it. The part I'm missing most about is the ion and exchange since we don't have the same media as say soil or coco. @Dirtbag just started flowering a week or 2 again so hopefully tagging him will get him to look at his changes in ph drift with the same buffer.

I still feel even a small amount ratio wise of ammonium/ammonia with the increased nutrient concentrations and uptake due to growth rates makes this more pronounced in hydro. You see during flower in soil the tendency for soil ph to plummet and it always attributed to nutrient build up or dying bacteria colonies but I believe there is more to it. The difference is these plant processes and everything else I listed are slower in soil as are the growth rates so I believe it's much less pronounced. The buffering capacity of course would be key and that's where I would lean towards adjusting. Of plant health is not impacted as long as you keep the ph in order than I don't see a need to fix it other than to find out the root cause.

Just my thoughts on paper