Clown Loaches get Ich pretty easily, but fortunately it isn't usually fatal. Raise your temperature VERY GRADUALLY and add 1 tablespoon of salt per 5 gallons. Then you can get a medication for Ich at your fish store. Take out the filter carbon while treating. The Ich should clear up after a while.
If you added salt to your tank already, watch your clowns very closely. If it was me, I'd vacuum the gravel and do a 50% water change to remove most of the salt. Clown loaches are one of those fish that has no scales, and the salt is very irritating to them. They don't tolerate it very well. However, article talks about using salt in treating scaleless fish with salt, so I recommend you read the article completely and decide how you want to handle this.
Here is another great article to help you decide on how you want to treat your clowns. There are a lot of choices. It looks like raising the temp. will work with whatever path you decide to take.
I had a clown loach die from ich, so what I did was put in strong medication and waited for about a week with the temp at about 86-88 F and then got a new clown loach and it doesn't have ich at all.
Clowns are very suscetible to ich. I have treated clowns for Ich just by raising the temp over 80F for 14 days and didn't loose any.
Just a side note Your clowns will out grow that 55 gallon very fast. That's a good excuse to get a larger tank