Sorry about your loss. Please cover the qt tank with eggcrate any time you have fish in there.
The main tank will need to be fed (very lightly) while doing hypo in the QT tank(s). Putting a sponge in the main (or main -sump) will grow bacteria over a period of a week or so. Bacteria will grow on all available surfaces. Just because your ammonia test reads zero doesn't mean that no ammonia is being produced. Fish waste, uneaten food, etc. all breakdown and create ammonia. The sponge filter will be a great home for the bacteria over time.
I put all of my fish (8) from my 125 in a 30 gallon tank for the 8 week hypo period. Lots of pvc
parts of varying sizes and lots of pwc
's helped. I didn't even botehr checking pH. I did 2x daily 5 gallon pwc
's for the first week, 1x 5 gallon daily pwc
's the secodn week, then 1x 2.5 gallon daily pwc
's the rest of the time. Yes, it's a lot of work, but I've been Ich free for over 2 years now.
I added an Ich magnet (blue hippo tang) last year, but it spent a full 30 days in QT before being moved over.
I had to remove most of the 200 pounds of LR
to capture all the fish for the move to the 30 gallon. Yes it was worth all the work to get Ich free and to remain Ich free.
Hope I didn't just jinx myself <lol>