The white spots on the filter sponge are not ich as I have ever seen or heard of it described. This will take a big more looking into.
As far as the nitrites, I am assuming these are because your tank is halfway cycled. You have grown a wonderful colony of the first type of bacteria - the ones that process the ammonia into nitrite, but there are not enough or none of the second type of bacteria that process the nitrite into nitrate.
These second type of bacteria are kinda touchy sometimes, and it takes almost twice as long for them to get going as it does for the first type to take hold. This unfortunatly leads to exceedingly high nitrite values. There are a few chemicals out there that can reduce the nitrites to a degree, but they cannot do more than about 1ppm easily - and you would have to be dumping a $14.00 bottle in the tank every day or so!
Your best bet is to do water changes. Everyday. AS much as you need to do to keep the nitrites down. Salt can help a fish having to deal with high nitrites. I would try a .1% salt dilution - that is 1 tablespoon per 5 gallons dilution. When you change the water only add salt back in for the amount you took out. Change 5 gallons, only treat 5 gallons to put back in.
If you can heat up your tank to 78 - 80 degrees, it sometimes helps get those bacteria growing a little faster......
The biggest key here is WATER CHANGES. Every day if necessary.
Please let us know how you are doing. I shall see if I can find any suggestions as to the white spots on your sponge. Lisal suggested that there might be pictures.....