Have you determined the cause of the ich? What was/is stressing the fish? That should be priority 1. Most fish can handle 30 ppm nitrates without harm for short periods. And how bad is the ich? A few spots? or fish covered?
Why are you feeding heavily? If you are trying to get medicine/garlic/ whatever into the fish with ich, try target feeding with a turkey baster. Fish are smart when it comes to food. Food comes out the baster? Then I want to be right there and eat from the baster. Fish are only going to eat x amount. If you feed heavily the drive to get their share actually decreases.
Doing 10 gal changes 2x week will help reduce the nitrates and will not effect the stress level. Make the changes from the sump. What are your current nutrient reducing practices? What filtering materials are you using? Polyfilter, carbon, purigen, skimming level? Dry skim small amount or wet skim large amount? How often are you changing the filter medium? Can you add macro algae to the sump to help remove the nitrates and provide food for tangs and other veggie lovers?
Sorry for all of the questions, but the sponge may reduce short term, but if you continue with large feedings and do not determine the cause of the stress you are just building an up side down pyramid - which will fall with a loud crash!
