I kept all my fish in 2 10 tanks with my LR
filling them up the backs, also made caves and stuff for hiding, with 2 huge HOB
filters with Carbon pads in on both sides, a heater in each, and a PH in each corner opposite of the HOBs. They had standard 10G NO lighting X 2 strips each. My tank which was way over stocked for my 55 - a small regal tang, kole tang, a royal gramma, a scooter blenny, a chromis, a peppermint shrimp... might have forgotten someone - it's been a while... I had to do this because of a tank crash as well... someones toddler dumped a plate of food in there *Yikes*
Anyhow, I tested once daily, did 1 gallon water changes 2 x week each (Mon & Thur) and I also reduced feeding quite a bit... every other day and smaller amounts to be sure it was all being eaten. I had the tank bare bottom and siphoned any debris off with the PWC
My fish NEVER got sick, died or anything ... they lived this way for many weeks due to the tank crash and a move.
Sorry to hear about your tank... hopefully whatever is wrong will be fixed and things will be much smoother next time