Your GH & Kh is too high! Cut with R/O water or run 100% remineralized r/o with GH booster. I recommend The Green Leaf diffusers they seem the best for Co2. Stop dosing Flourish & switch to 100% EI dosing with Plantax with boron to add trace. Stop dosing Excel if your dosing EI. 80% is too large. Your chasing your tail. 50% is good enough. Seachem Prime irritates fish from my experience I simply do not use it anymore.
I have the same water you have. Before switching to R/O water I had all kinds of algae & sick fish. The water is too hard & your Kh is through the roof. There is nothing you can do about it. I would strip it down to nothing & build it back up. Do 50% water changes 1 time a week. With that kind of volume you will be using a massive amount of water. I am still not rushing my 55 for that same reason. My 10 is doing great now with EI dosing & 6500k bulbs with Flourite substrate. All I use now on my tanks are 100% remineralized water. I would never go back, the liquid rock, you can have, nothing but problems.