PLEASE HELP !!! My PH keeps dropping everyday (DWC). What causing this?

lock in your water temp and this will all be solved

Say it like it is numbers. lol

A rapid drop in pH (pH drift downwards) in DWC/hydroponics or coco/soil substrates is almost always caused by a combination of microbial activity, acid accumulation/salt buildup, or the uptake and release of ions by the roots (roots release hydrogen ions H+ when taking up ammonium or other nutrients). Here are the most effective ways to keep the pH stable in your reservoir or substrate: 1. Use an EC/pH Buffer (Tap Water / CalMag)If you work with RO (reverse osmosis) water or very soft water, the water lacks a natural bicarbonate buffer (KH). As a result, even a tiny amount of acid can cause the pH to plunge dramatically. Solution: Aim for a base EC of :text.2 - 0.4$ mS/cm by mixing in tap water or adding a CalMag supplement before adding your base nutrients. This buffered water absorbs fluctuations much better. 2. Check the Type of Acid (pH Down)The type of acid you use to adjust the pH makes a huge difference:Phosphoric Acid (H3PO4): Ideal for the flowering phase and much more stable in reservoirs. Citric Acid: Very unstable in reservoirs! Microorganisms break down citric acid within 24–48 hours, leading to wild fluctuations. Avoid using organic or citric acid-based pH down in hydroponic reservoirs. 3. Aeration and Water Circulation in the Reservoir Cleanliness & Organic Matter: Bacteria breaking down organic matter produce acids that lower the pH. Make sure your reservoir is light-proof (to prevent algae) and clean it thoroughly every 7 to 14 days. Circulation Pump: Use a small wavemaker or circulation pump in the bucket/reservoir to keep nutrients and pH adjusters constantly and homogeneously mixed.4. Determine if the Plant is Getting "Too Much" or "Too Little" NutrientsChanges in pH often directly indicate how the plant is responding to the nutrient concentration (EC) in the reservoir:

A pH drop of 0.5 a day in hydro isn't a calibration problem, it points to the root zone. Brown-orange roots and dark water suggest early root stress or pythium, which would also explain the yellowing, droop and stunting. Your pH of 5.6-5.7 is still fine for hydro, so it's not a lockout. Check reservoir temp first, keep it at 18-20°C, add more oxygen, do a full reservoir change and clean everything. Add Cal-Mag only after the roots recover

To try and keep it short, not simple, your drift in PH is exactly what you want and the range you want it to be in, between 5.8 - 6.2. Half nute strength is great. Keep at least 1-2” space between your roots and the top of your water. Always use an inoculant like Hydroguard. Change your reservoir with every nute change. Try to keep your water temp below 70 degrees. One of the most critical things you will do is supply oxygen to your plants roots through bubbles. More bubbles the better. You want it to look like boiling water if possible. Then you have to deal with all the other environmental problems and solutions, lighting, temp, rh, etc.. From the picture your plant looks overwatered. Meaning you top off too close to the bottom of your root bucket not leaving enough air space for the plant to breath, so it thinks it’s drowning. That along with not enough oxygen to properly take up nutes, and you have a dying plant no matter what other conditions you give it. I grow DWC and have been there starting off, it’s an experience, once you learn and understand it you will be amazed just how fast it grows. Good luck.

humidity is on the low end but if this was in soil they look over watered, wind burn, nitrogen toxicity but I'm not a hydro guy good luck

do you have some sort of regular drain, clean and refill process? topping off is fine for a while, but the plant is selectively taking in certain nutrients, so the balance always skews over time, which can impact pH. is the water warm? What's the discolored stuff at the bottom of your murky water? that might be stained roots, but is it slimey? smell? if either, it's growth of microbes. looks like something gross on the lid, too. can't be sure, but give it a good clean and refill. Maybe some h2o2 for those roots. A ~700ppm (not counting hard water, calculated from labels) diet is all you need.

Sorry - one more thing. I see you have very little air in that huge reservoir. There are barely any bubbles in that pictures, you don't have a diary. Just going by what you provided. You likely need a bigger air pump(s) and more airstones.

My two cents. I only do very small DWC reservoir, so my situation is different. First: PH drop is fine in that range, you have a massive RDWC so it will be more difficult to keep steady. Plants naturally get a variation in PH and is actually pretty beneficial. 5.5 to 6.5, a slow natural drift is a sign of active plant feeding and normal root-zone respiration. When Drift is Dangerous: If the pH plunges below 5.0 or spikes rapidly past 6.8–7.0 within a few hours, it points to underlying issues like root rot, heavy microbial/algae growth, severely imbalanced nutrient strength (EC), or improper source water alkalinity. Second: Roots look pretty great except you have very little space between the bottom of your net pots and water level. You want to have at least 1 inch space, it can go even more like 4 inch if the roots are still slightly submerged. As water level drops the plant naturally will grow longer roots, grow stronger and be able to tolerate the drop. Third: I do think you are over feeding!? Less is more, I have had much better success letting the PPM drop about 100 PPM over two days then I top up with fresh water (I use RO water, so I also add CalMag) and then add just enough nutes to bring the PPM back up. Hydroguard beneficial bacteria significantly improve nutrient intake and availability for plant roots. This means even less nutes than you might have thought before. You will not see a huge improvement with those plants very fast, they will only start to grow new nice leaves. I wouldn't count on the damaged ones to fully recover. I truly hope this helps? Just trying to help, took me years to learn all the quirks. Stay strong and carry on brother!😉💪👊