pH Keeps Rising By The Hour. Please Help!

Hey “growmies”, need some urgent second opinions.
Currently running an 8 plant recirculating top drip fed system, feeding for 20 mins every hour. Rockwool and hydroton as medium.
Rez is 60l (~13 gal). I know its a bit small for the number of plants (was planning on a sog type set up) but bearing in mind they’re only baby girls right now at 1.5 weeks old.
RO water. Res temp hasn’t exceeded 20C/68F.
Running Canna nutes (vega a+b, calmag and foliar spray rhizo right now) with calcium hypochlorite at 2-3ppm for “sterile rez” - yes I know it’s not completely sterile but keeps bacteria at bay.
Temp in room 18-23C/65-73F over the course of the day and night and RH at a stable 50-60%.
My pH keeps rising every hour or two by at least 0.5-1. Before bed I take pH down to 5.2 and by morning it’s around 8.
I’ve ran a few experiments, they are as follows.
Took fresh new rockwool from the same batch I’m using and added it to water and let it sit for a day, pH rose by about 0.1 so I assumed it’s not the rockwool. Did the same with hydroton no rise there so I don’t think it’s the medium, I washed it a few times before use too.
Removed my powerful air stone for a few hours, pH still increased in the res so assumed it wasn’t due to air stone (using a rubber one too no calcium rocks).
My only current theory remaining is that there’s just too many plants for the size of the res so as they’re consuming nutes it’s increasing pH. However they’re only tiny babies so surely they’re not taking the pH up to 8. If I’m wrong then how much worse can I expect this to get when they’re older girls using way more nutes.
Thinking of investing in a good blue lab auto pH but I feel that won’t be able to deal with the massive swings and the alarm will just keep going off.
Please correct me if I’m wrong at all and any advice would be greatly appreciated.

Now trying to increase my nutrient content in the water to act more as a buffer in case it is the plants utilising nutes and raising pH. However, I’m doubtful as my EC/PPM hasn’t changed much. Will update.

Are you using bio canna ? I had this same exact issue and tried everything you did. The only fix was to aerate my water for two days first and then use synthetic only nutrients. Removing all organics. When plants where young, I still noticed some rise but I could now make it 2 days within range at least. So I'd start at 5.5 pH and then it would rise to 6 in a day and another day would be half the jump and be 6.2 and then slowly stopped rising after it go to around 6.7. however after another week or two when the roots really started to fill my 5 gallon DWC. From there on I would see little fluctuations. It would rise just a very little but now manageable and would level out faster and stay consistent. Maybe give the aeration a try first but using organics I think is def going to create change over time. Hopefully someone else can give you some input to but aerating my water for 2 days before use with air stones seemed to make a big diff the the nutrients switch to Flora series from general organics made a it all come together. Good luck hopefully something I said helps u

Why would you want to use organic nutes in hydro? You're just setting yourself up for failure if you do.

It sounds counter productive to me to run organic with a hydro setup.. I run full organic, with soil and microbes, the way hydro runs I would be worried it would kill the microbes. I would stick with synthetic if you are running hydro, run organic if you are using soil.

ExclusiveX420 said:

Are you using bio canna ? I had this same exact issue and tried everything you did. The only fix was to aerate my water for two days first and then use synthetic only nutrients. Removing all organics. When plants where young, I still noticed some rise but I could now make it 2 days within range at least. So I'd start at 5.5 pH and then it would rise to 6 in a day and another day would be half the jump and be 6.2 and then slowly stopped rising after it go to around 6.7. however after another week or two when the roots really started to fill my 5 gallon DWC. From there on I would see little fluctuations. It would rise just a very little but now manageable and would level out faster and stay consistent. Maybe give the aeration a try first but using organics I think is def going to create change over time. Hopefully someone else can give you some input to but aerating my water for 2 days before use with air stones seemed to make a big diff the the nutrients switch to Flora series from general organics made a it all come together. Good luck hopefully something I said helps u

Click to expand...

Thanks for the reply! Not using organics, normal canna aqua range, running a sterile rez so my calcium hypo would kill off living organisms so using synthetics. Appreciate the advice though!

Update: the increase in nutes didn’t pH buffer. Had a rise from 5.5 to 7.3 in under 4 hours. Still a mystery

Use different nutes maybe.

I put jacks in ro water and with a weak ec I get 6.5 ph or so. The stronger I make it the lower it gets. Ph in water rises with an air stone in it naturally but it should only be a few points and then stabilize.

Are you able to use straight tap water?

Try that for a few days. No nutes needed if the plants are very small and the tap water is ok.

Are you using tap water?
Hmm. Is there any information on your nutes that suggests a waiting period before adding pH solution? I used UC Roots to combat an issue previously and it specifically says to allow a waiting period B4 adding pH and I honestly had weird issues trying to adjust pH until I really let it settle and re aerate a bit before putting it into my DWC pot. Then added pH later. I sware I added more pH than ever a few times for it to nearly stop dropping at 6.3. I got it down to 6.3 then adding more pH down was basically not changing the pH anymore ( I only added up to 5ml before I stopped thinking something was wrong) to find out later on after a day in the system it was re checked and 5.6 is what it ended up being. Thought it was a pH meter issue. Def wasn't. So, sometimes that can be it. I would use two bucket with half of your water amount in each and add the nutes 50/50 to each bucket mixing well each at a time. Some micro nutrients are suggested to be added before or after mixing all nutes. These details can be a factor potentially. I now use hydrogen peroxide with every pot. 3% food grade at 2.5ml per gallon to help with root issues, fungus or rot. Highly suggested to put the peroxide in 1 bucket with half the water and mix nutes in the other half then mix the two together, then add pH adjustment. Otherwise, improper mixing can occur and false reading or reading that will drastically change can happen.
No problem I'm not a pro but have had these issues and battled them for the win. Never used a recirculation system but dwc with alot of air stones should be somewhat similar.

I’m using RO water with calmag supplement. My tap water is around 0.7 EC on its own so no way I can use that.
Might switch to different nutes see if that’s the cause, thanks for the advice.
Nothing on my nutes about waiting to pH. I’ll give it a try though. Always add them in the correct order allowing time in between nutes and mixing thoroughly.
Yeah I also recalibrated my pH pen twice and then bought a new one too. Wasn’t the pH pen ahaha.
I used to use hydrogen peroxide for sterility but it got too expensive when compared to calcium hypochlorite. Got about 5000 doses to make 2ppm in res of cal hypo for the same price as 1L of 3% H2O2.

Thanks for the advice everyone, much appreciated!