Joel
I find the wood-I's tend to have more deflection than the old style wood framing. Floors tend to sag a bit over time aswell. I'd wonder how level the tanks would sit once filled and a few months have gone bye. Is it too late to consider changing plans on tank location?
Also ambient temp is another consideration unless you have A/C or a chiller for the warmer weather. My tank is in my basement with a chiller.
You probably already considered all this but I just had to open my big mouth again. Good thinking by adding the extra joists.
Good luck with the new house
Kari