Do you have a 24 hr. Petco or Petsmart? If you could get more salt and just make clean water...Or Amquel, a water conditioner.
You are having a recurrence of the cycle. Each fish you put in, individually, causes a mini-cycle, sometimes not easy to detect, but it happens, on a new tank. Add a little overfeeding and it's a much bigger problem. A 10gal is very precarious in terms of margins. What you need is bristleworms to take care of that overfeeding, and snails and hermits to help keep the tank clean: your inverts should always mass about 3x your fish load. Is there anywhere including calling friends at this hour that would get you some sea-salt? You could get distilled water at an allnight market and use 1/2 cup per gallon salt, remembering to mix extremely well [ a pump is the best mixer] and just put the fish into qt, even into a clean spare bucket with new salt water. Clowns are tough, and he might make it.
Do not think of starting over: there's nothing wrong with your tank except over-stress by too many fish too fast. They quit eating when ammonia/nitrate rose, and they're still suffering from it. Redoing the tank will just mean a whole new cycle. THis one is nearly complete.
some 24 hour groceries sell sea salt for human consumption in with the rest of the Morton's salt, etc. They also sell distilled water for steam irons and the like. I'm not sure it's the best idea, but if you have absolutely nothing else, use half a cup of that salt to one gallon of water, and be absolutely sure the salinity is equal in tank and in new water, and that the salt is completely mixed. I'm telling you something that I wouldn't do unless it was absolutely the last chance for this fish, and it may be. I can't stress enough: completely mixed until the water is clear again, and same temperature and same salinity. This fish is right on the edge of not making it.
Always have salt and fresh water and a spare container that can be used as a qt tank on hand: an old cd cylinder will do in a pinch: emergencies have a way of reaching crisis after all the stores have closed. I wish you luck, and hope he holds out til morning.