The tank is ~770 gallons. It's bigger than it looks thanks to a large front-back dimension.
I was involved in the initial system design, equipment selection, working with the tank vendor (Miracles), fundraising, etc. The volunteer project team fell apart right around the time the tank was delivered (our leader moved out of state and the Museum's project manager left, so we pretty much lost contact) - I'm not sure who ended up actually building the system or who is maintaining it now but I'm glad it looks so nice.