Dt hypo treatment

[George]

I wouldn't do hypo in that large of a tank. First of all, you still have to take out a lot of salt water to replace it with fresh water. It's not that much more work to just drain the tank enough to catch all the fish.
Second, there will be a lot of die-off's in your DT if you have live rock, live sand in there with hypo. You skimmer won't work in hypo. A lot of organic. Ammonia will be a problem. Dosing ammonia binding thingy will get expensive in that large of a tank.
Also there are some researches showing that a certain strain of marine ich can survive below hypo salinity. Your chance of getting that strain may be low, but still a chance...
good luck with whatever you decide to do.