pH dropping in nutrient reservoir

[YukonColin420]

I have an auto feeder setup for watering my grow in which I batch my nutrient water to run for a couple weeks off a timer. Over time the pH level in the reservoir slowly drops off from 6.0 to as low as 3.8 in two weeks time if not maintained with pH up. The solution is prepared from reverse osmosis water and general organics nutrients and pH up. Reservoir has a circulation pump and aeration, no issues with algae or anything. Just wondering if the drop in pH over time is normal? Oddly enough in my old DWC setup I had a constantly climbing pH... lol. Any input would be greatly appreciated. Cheers!

 

[golfnrl]

I grow in the autopot system using a 12 gallon rez. The PH tends to drop, not rise. I bought a PH controller to keep it steady. Have you always used aeration? Is that an air stone? I don't use the stone anymore as I found it caused the PH to be unstable. I have a small circulating pump timed to run every 6 hours for 10 mins. That and the controller stopped my PH issues in the rez.

 

[3Berries]

Ambient CO2 causing the pH to drop with the aeration? If I use rain water for nute mix and don't add some disinfectant (H2O2) and if I add molasses it starts to ferment. The CO2 fizzes away and the pH keeps falling.

 

[YukonColin420]

@ golfnrl Thanks for mentioning the stone as a possible cause, I didn't consider that yet. I'll try removing it and replacing with a glass diffuser and see if that helps at all. I was considering the pH controller too, but if I can reduce the amount of pH maintenance required without spending more money that would be optimal. 😁
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[Bluey]

Don't aerate your tank.
EDIT: Correction...you're hydro styling it....thought you were coco growing...do aerate

 

[DW2]

Howdy Yukonolin420, in my DWC setup, the pH changes as the plants take up the nutrients and I keep four 2 inch by 4 inch air stones running 24-7 in the six-gallon reservoirs. I do not 'chase' the pH up and down, I only adjust the feeding solution pH and the mid-week top off water to 6.0 and allow the pH in the reservoir to fluctuate because, as said many times on this site, different nutrients are best absorbed by the plant at differing pH levels.

 

[bboyfromwayback]

My ph tends to rise. I purchased a bluelab ph controller and it works great. Keeps the ph right where I set it

 

[Bluey]

I have a 27 usable gal reservoir and I drain to waste. I won't pump air through it because of the pH issues but by the time I finishing mixing it is at its saturation point re dissolved gasses.
pH still moves a little over a 5 or 6 day period depending on how I mix and buffer it but I can get it pretty stable over the two days I'm home. It will only move about 0.1. No more than 0.2pH.
Make sure your reservoir cannot let in any light, big mistake if it can.