Quarantine.. It's a parasite... just one ICH spot will multiply and cover your own tank. It doesn't "calm down"... you're not treating the fish, you're treating the water in the tank. See, you can't cure ICH when it's on your fish... only when it's in the water. you do NOT want this in your main tank.
If treatment is too much trouble, then return him and don't buy another from this tank.. assume that ANY fish from that tank will introduce ICH and need to be treated.
For one spot, I wouldn't bother with the salt method...
I used AP's Quick Cure at about 60% dosage and my Loaches did just fine. However, I can't say how yours will respond, so if they start to show stress or acting ill, do an illediate 30-50% or more water change and go with another method.
In a 10 gallon hospital, I'd remove the carbon, set the temp to 82(start with 5 drops of quick cure(or half done.. depending on consentation... the bottle will tell you how much is a full dose) and see how it goes. You're going to have to do water changes every couple days(I did about a 20% change before every other day, and I treated every day at about the same time.
IMPORTANT! Do NOT stop treatment when ICH disappears! This is when it's spreading, and is the most critical time of treatment.
There are three stages in the life cycle of ICH... when it's on your fish, you can't kill it, you can ONLY kill it when it's free floating/looking for a host. This is when you can't see it! So treat for at LEAST 3 days prior to giving him the all clear, preferably 5 or 6 days. Then do a 20% water change and lower the temps back to normal and give him several days to see if it comes back.
One other note: You're raising the temps to speed up the life cycle of the ICH, do not raise the temp until you begin treatment. By raising the temps, you can dramatically speed of the process.
So pay close attention to your tank when the spot disapears... and continue treatment for at LEAST 3 days, Preferably 5 after you don't see ICH in your tank.