Critical Orange Punch

all PH water no nutrient, looking amazing, smelling very gassy. Throughout the grow I was fighting PH issues, on a daily the PH would drop to 4 and I would bring it back up to 6.3-6.5, I tried many different things to fight the problem, pen calibration, res cleans, roots dunked in peroxide mix, doing no PH adjustment to see if there was something in the nutrient causing it and I also tried without nutrient just plain water, everything I tried had the same result PH of 4 by the next day. the water level hose would get occasional algae in it that I would clean but my research has lead me to believe this will not cause the PH issue, so I am really left with root disease , although my roots were a lovely white-light yellow and there was nothing visible to the eye its the only thing I can think of that would cause the PH issues and during veg I did encounter a period were my water temps were very high, if you have any experience with this problem please comment, unfortunately got very hard to take root pictures once I put the net on so I apologize for lack of root photos. As I maintained this PH problem daily in my opinion it wasn't as much of a problem as it was an annoyance, I believe I would have had closer to 1g per watt with a stable PH, but non the less I am very happy with this grow