As NC said really
If you do have carbon in the filtration system remove it, this absorbs most meds that are put in
This was my routine for treating ich ....
A massive water change, get as much daily debris out (basicly make the tank mint looking lol, including wiping plants/rocks etc down to get any buildup off them) then top up with fresh dechlorinated water (i always use an aloe vera type)
Slowly raise temp, add meds (i have used el cheapo to expensive and got results from all) add salt at correct dosage (google's your friend if no salt-dosage sticky on the forum)
Make sure whichever meds you use you follow the dosage to the drop and the time intervals too
This is critical with the ich having a time cycle, as you wanna zap the l'il critters when their at their most vulnerable
The most i've ever had to dose for ich was a two-dose cycle (i mean not double dosaging the meds, but having to go through the treatment stage a second time) , i couldn't get any aquarium salt at the time and a few fish still had ich signs, but the second dosage run sorted things
While i mention salt, an old way was to salt bath the fish if really bad with ich, again, it's searching for the correct dosage and time in the solution which is the key
I use a pond product now, only because i have a large tank and it works out way cheaper than the smaller sized small tropical fish tubs/bottles
It's called Waterlife Medizin P
Treats Ich/Velvet/Costia trichodina/Cryptobia
This works out cheaper for my 6x2x2 if ever i get and problems compared to the small 100ml bottles they sell at my lfs's
If you can, maybe post about specificly salt bathing for ich, i have come across stories where this seems to cure ich very fast
Food for thought
Goodluck (dang ich grrrrrr)
Def