Falling PH

[Bryan]

I am running a bubbleponic system with a 6 gal res, and a 400 wt hps light. I'm 4wks into bloom everything looks good but the ph keeps falling. I adjust water to 5.8 at start of res change,by morning ph is around 4.8 is this has happened last two res changes. Is this an indication of something going wrong? I'm too close for something to go wrong now HELP

[DW2]

Welcome Bryan to the forum,
The pH of the water, with the nutrients, should be at 6.0 +/- .5. Get a pH meter or a litmus test kit and check the water and adjust it up or down as needed. The pH will normally drop as the nutrients are used by the plants. I run two set ups similar (only with CFLs) to yours and I balance the water when feeding and at mid week when I top off the tanks. If the pH gets and stays too high or too low, the plants will stop absorbing the nutrients and will wilt. I almost killed some of my last grow by being too impatient and trying to adjust the pH in one of the tanks mush too quickly. It is best to make gradual changes than to do it all at once. If things do get out of hand, like during my last grow, just drain he tank and refill it with pH balanced water.
Good luck with your grow.

[DWC4ME]

Are you adjusting before or after nutes? If after good, are you letting the rez sit for about an hour or so before checking and adjusting PH? I had the exact same problem, I would start with water, add nutes, measure PH, and adjust. Next day low PH. After some research I found out letting the rez settle before adjusting made a world of difference. I was checking my PH immediately getting, this is a made up number, say 7.3, I'd adjust to close to 5.8 next day like you in the 4's. After letting the rez settle my PH was actually much lower. I was using way to much down. I went so crazy I now have 3 PH pens. I blamed it on the pens giving me bad readings. I honestly have about $150 in pens. Lol. Hope that helps.

[PigSquishy]

I do not know if this will help you, but according to the brand of nutes I use they want me to set the pH at 6.00 and then let it rise and fall between a pH of 5.50 - 6.50 without any adjustments, as different nutes are best absorbed at different pH levels within that common pH range and if you do not let it have a pH swing you can run into nute deficiencies. There has also been times I've ran into issues with my pH swinging like yours because of Cal-Mag uptake. Another way I found to stabilize the pH was by switching from pH Down (35% Phosphoric Acid) to the strongest pH Down you can get and after that change my pH is now stable 10-minutes after mixing and stays stable within the proper pH range for the rest of the week every time. This also reminds me that in hydro I've seen the pH have issues when algae or something like pythium has hit the plants. Yet another one I can think of when my pH has done had issues like this is when the water temps got to warm and the oxygen in the water wasn't high enough which caused my nutes to break down faster and led to pH issues. This could be as simple of an issue of needing to do a water change as well as your plants are using lots of nutes right now and crashing the pH because of it.