You definately want to remove the Carbon as the previous post states, it will remove the treatment you add.
Its not something to sit out, if you've been treating for 2 weeks and no improvement something is wrong I suspect with the water quality.
So I was wondering what water changes you have been making? I would be making small regular changes and taking Ammonia and Nitirite readings, something like 15% a week increasing from here if you have any Ammonia or Nitirite readings. You can change a larger amount a third if the readings are high, just make sure you add the new water in slowly if you don't have a spare heater to heat it seperately.
If you increase the temperature you make the parasites life cycle shorter which will bring the disease out quicker on the fish so you should be treating with the recommended dosage not a weaker dose as the disease is at its most productive. Typically most treatments you buy are safe to overdose as they weak versions of chemicals such as Malachite Green. I would buy a treatment which has this in. I've used TAP chemicals with success
I wouldn't be feeding them whilst under treatment and I guess you clean any filtration with used tank water?
I've found from working in a fish shop from customers, if the breakout of whitespot isn't brought in on a new addition its stress related so poor water quality caused by over feeding or cleaning the filters uner the tap on a well stocked tank causes the water quality issue weakens the fishes defences and lets the ICH take hold.
Hope this has been some use.