Just a recommendation. But I noticed the two 55 gallon drums for the water change system. Is that going to be the only water storage system you have?
If so, id recommend rethinking that. For your size tank, I would have a min of two 400 gallon containers.... Putting that much money into a tank, if something major every happened, you will be wishing you had more fresh made up RO water on hand to do a major water change.
I have a 300 gallon, and have two 250 gallon containers, one for RO, the other for Salt...RO is always toped off..just incase something happens.
again, just a sugestion