Thanks for the responses so far. With respect to the CO2, I was hoping the DIY would work because the tank is only half way fill (approx 35 gal). I have the mangroves growing as emergent vegetation. I was also going to supplement with SeaChem Excel Organic Carbon along with the DIY CO2. Any opinions? Also, does anyone have an opinion on whether I should switch my water changes to tap water instead of RO/DI? I know if I dose the CO2 that the pH drops in the RO/DI to around 6.0, so maybe I am answering my own question :?