If you don't/can't take them back:
1. Lower the water level to permit lots of splashing, or add an airstone.
2. Buy some Ammo loc, or another product that will bind ammonia.
3. Read
THIS
4. Do small water changes daily or every other day until your water test kits show NO nitrItes.
And hope your clown makes it. Loaches are quite sensitive to water quality and should NOT be used to cycle a tank. However, that is what you are currently doing. Read that link in #3. Then do the best you can, and let us know how it goes.
The 'discolorations' in your pic may or may not be oodinium. I wouldn't jump to trying to treat for that just yet. Get your tank cycled FIRST. DON't add any other fish until you have completed that process, and see if the fish that are in the tank already make it.
Did your Local Fish Store (lfs) tell you it would be ok to put clowns in a new tank? If so, shame on them. What size is the tank, and what else did you put in it? what is the temp? Can you go get some testers? At least the cheapo test strips that will tell you ammonia levels?
And azrael181--no one here meant to be rude. We are here because we have a significant interest in fish. Loaches in particular. We know that you likely got bad information and now are here looking for help. It is frustrating in the extreme when we run into the same scenario over and over again. LFS gives new fishkeeper the ok to bring home loach to new, uncycled tank. New fishkeeper discovers his fish are having problems. LFS says, 'sorry, we don't take back fish'. New fishkeeper finds forum and hopes to get a magic solution to his/her problem.
Unfortunately, there isn't a good replacement for doing your investigating before you buy. But the lfs won't tell you that. Most of the time they just want to sell you fish. Besides, if your fish die, then what do you do? You go back and buy more fish...
hth....