are you saying the display tank is 55 gallons? or you have a 55 gallon hospital tank?not a good idea to do hypo with anything but a hang on filter. (bare tank) you can get some coffee cups or 4 inch pvc in there for the fish to hide,it really sucks when a new guy wants a salt tank and adds a fish with ich.which over almost 30 years i have been doing this almost 50+ % of fish have is when we get them. you my friend are in some trouble.if you can go get a 10 gallon tank .put the inverts in it with a good powerhead. .you need to empty the dt .get another hang on filter.buy some amquil for ammonia.you are in a tough spot to save these guys. i can go on for two more pages about a qt for new fish ,the life cycle of ich and salinity.but right now if you want to save these guys you need a 2nd tank. sorry