well, let's see here....
I am fairly sure melafix can be used with your bio wheel still in place...let me look, i have the box...yes, it says right on it "will not harm the biological filter" so, you didn't need to take it out in the first place, because if it dried up, then everything is dead for sure. oh, btw, the melafix is an all natural antibacterial agent made from tea tree oils and the like
second, bio wheels dont need to be replaced. The worst thing that could happen would be that all the bacteria dies and it just has to recolonize...
do be careful about how much salt you add because too much salt can harm freshwater fish. If it didn't, there would be no distinction between freshwater/brackish/saltwater.
also, bear in mind, that how much fish a tank can maintain doesn't really go by how much room it looks like there is to swim. It goes by how much waste the fish make (bigger fish make more waste, so they are the equivalent of many little fish)
just curious, how warm is your water if you don't have a heater...because that is a big deal...as are the test kits.
the thing to do would have been to get the heater/test kits, etc. when you set up the tank, or before there were fish in it since it is necessary to monitor the water parameters, but thats not an option anymore, now is it
so the best thing to do is keep up the water changes and maybe add some stresscoat if you have it and keep your eye on things. Also, if you replace the blue filter as well as the biowheel, you will remove almost all of your biological filtration = that is where all the good things live.