Are you in flower or in veg?
Properly maintained, ph should naturally go up in veg(plants eat more N than PK which raises ph) and naturally go down in flower(plants eat more PK than N which lowers ph).
Regardless, if it’s increasing ph really fast, like overnight, it could be bacteria in the water. Bad water increases ph very quickly. Usually able to smell it too, like dirty socks. Healthy roots smell spicy. I usually run my reservoirs sterile using calcium hypochlorite, or bleach in a pinch.