1. What does your drop checker say ? Seems awfully small amount of CO2 for such a large tank.
2. For such a large tank, I very very very very much doubt a glass diffuser will get anywhere decent enough CO2 levels and distribution.
3. Your water is awfully soft, which again leads to many issues. Try hardening it with tap water or calcium carbonate to at least 4dKH, even better 8.. With soft water and CO2 you are never far away from pH crashes and associated livestock issues !!!
4. What level filtration are you using as well as spray bars etc ?. For a high tech tank with CO2 you will be needing a filtration rate of at least 700 US G per hour, to stand any chance of enough flow and distribution of CO2.