I have a couple of questions which may help you treat better. First off, do all of your fish have ich? Secondly, do you have another tank that you can use as a medical tank? (Doesn't have to be big)
I would definately do another water change ASAP. I would suggest AT LEAST twice a week water changes, but more like every other day. If your tap water isn't too different (pH, KH, etc.), I'd do about 50% water changes every other day. In a Medical Tank, to treat for ich, I've gone as far as to do every other day 75% water chages with throrough gravel vacs. Gravel vacuuming is VERY important to remove eggs and Second-stage of ich (Free swimming). I would also fully dose the tank with medicine each day. Many disease-based websites say to change 75% daily and redose fully daily. I would be willing to do that if I wasn't so lazy. I, personally have only used Quick Cure (for ich) and Coppersafe (for parasites- which turned out to be planaria

) I would only raise my temp to about 82 degrees and would keep up my treatments for 2 weeks, regardless of what it looked like. I would then keep them separated in the medi-tank for another 2 weeks (total 1 month) to make sure I got it all.
To sum up:
- Use Quarantine/Medical Tank if possible, and only treat those fish affected. Raise temp and perform water changes/gravel vacs on main tank also while treating, even if using medi-tank. (This will rid main tank of ich while treating only the affected fish)
- At very minimum, I'd do two 50% water changes weekly (say Wed. and Sat.) The more often, the better.
- Add one Tablespoon/5 gallons Salt to aquarium. I know people say that Catfish and such don't like salt, but mine and several friends have used this and our plecos and catfish are fine. (disolve in water first for sensitive fish)
- Raise temp to 80 - 85 degrees.
- Choose one Ich medication and stick with it. Dose fully daily. Don't mix medications.
- Add Melafix (I only add after water changes, not necessarily daily) This will help "naturally" keep minor infections from occuring and promote slime coat. You CAN mix this with other medications (it is 100% natural)
- Relax and be patient. If you panic, you make poor choices. I used to panic and killed more fish with my intervention than diseases killed.