DWC Coco croutons - pH rising every 12-24 hours

I've been hoping this issue would stabilize but it doesn't seem to be. I'm wondering if my Res change added insult to injury or was a step in the right direction.

I've been pHing the water down to 5.6. This is tap water that comes out at 7.5-7.6 (sometimes upwards of 8.0), and a ppm of 140-170.. 90% of the time in the 140's. Water hardness has been tested in the past due to fish tanks and is around 7. I let the water set at least 24 hours before going in the res to help evaporate any chlorine.

Within 12 hours... I'm am always in the 6.2-6.4 range. Is this because of something in the coco croutons that I did not treat because I found no information on a pretreatment being needed? Or should I be chasing another issue? Its new rubbermaid tote... could that be it? Maybe the sealer/expoxy I used to seal the hole for the airlines that is below the water level?

Tomorrow will be 7 days I've had this system going. Two days on the res change. Just seems like I shouldn't have to go through so much pH down. Because of it my PPM's go through the roof and once it hits 700-800 ppm I feel the need to change it. These are still basically seedlings so I'm only feeding them 150 ppm of nutes at this point.

Thanks for everyones time!

there will usually be a fluctuation in pH over 24hrs when growing just embrace it. I find it best to PH down/up every 48 hrs or when you top off with fresh water to keep things under 6.5 and above 5. Hope that helps

Is it really ok every 12 hours though? I let it go 24 hours to this morning and it was at 6.5 - that is really ok?

Seems like it should stay a little more stable. I'm still in the learning phases with this hydro stuff though so maybe I'm just being paranoid.

Your ph should rise but not that much in 24hrs. Well mine doesn't anyway.

If you using a tote then check for light leaks or if the plastic is thick enough so that outside light doesn't illuminate the root zone. If possible stick it over your head (obviously when empty ) and make sure it's complete darkness.

Algae will grow if this is the case and cause your ph to rise.

The light thing makes perfect sense to me now. The tote has been covered in foil tape... except for the bottom. I currently have the tote elevated so the tote could receive light from the bottom, but that would be the only place. I havent seen any algae though... so if it isn't present... is that really my problem? I've had fish tanks for years... so I definitely know what that stuff looks like even in its earliest stages!

Thanks for the tip about not putting it over my head while full

I taped the crap out of the bottom with the foil tape as well as the top of what it is sitting on so it doesn't transmit light from underneath that way either. Also added about 5 ml of h2o2. It only moved .1 pH in the last 5 hours... I think we might be on to something!

Just an update for anyone that stumbles on this thread because they are having issues with their coco and pH.

In the future I would make sure to soak that coco overnight in pH'd water. My pH has been getting more and more stable.

My only concern remains to be if the coco can support the plant at full flower/maturity.