Dwc is generally unstable because you have gallons of roots sitting in only ~5gallons of water, constantly. The bigger reservoir, the more stable it will be.
It’s why I switched back to flood and drain. I have a res that holds 20 gallons and since the roots only touch the water for 1 minute every 2 hrs, I can leave for days at a time without touching it.
Again tho, if you’re in flower doing dwc and ph is raising, likely need to go sterile.