Looks good so far. The giant danios look really large.
You're using a paintball CO2 system on a 75 gallon tank with a HOB? Does your drop checker ever reach green?
The HOB is an auxillary filter. It's not even running these days. I'm running the C02 through an Odyssea canister's intake. It's pretty efficient at 3-4bps. I accidentally gassed one giant danio and a few albino zebra danios the other day at 6-7bps. I estimate that I'll get at least 8-10 weeks per 20oz tank at 3-4 bps. My gauge hasn't moved off of 800psi in the weeks since I started using it daily.
The paintball C02 idea came from this thread
. I got the tank from my son and I have about $25 in the ASA on/off & the fittings/gauge. Not bad... After the initial $25, I'll get pressurized C02 for ~$2 a month.