Ick is an opportunistic infection from stress and/or poor water quality.
You can't dose that med in a cup. It's too harsh on him. Sounds like you've overdosed him. You need to dose a full gallon jug and then use the jug for water changes - needs to be prewarmed and kept same temp as he's in. IMHO, there are better ways to treat ick..
The best way to treat ick is to slowly at no more than a degree per hour raise the temp of the water to between 86-88F. Leave it there at least one week past
the last sign of ick. Salt is optional but can be used at 1 tsp per gallon predissolved for up to 10 days. You can't use salt with invertebrates, some smooth skin fish or live plants.
In a new tank you need to be testing daily for ammonia and nitrite using a reliable drops kit and doing a 50% change any time you see any ammonia or nitrites show. In addition to this you should do a weekly water change of 50% with siphon. You would see an ammonia spike first, then nitrite. Eventually ammonia will fall to 0 followed by nitrites and then a once weekly water change of 25-50% with siphon will be needed. Cycling can take up to two months: http://www.bettafish.com/showthread.php?t=47838
Always make sure water changes use same temp water (use thermometer to match running tap) and are also pre treated with conditioner before adding to the tank.