[JWarren]

Looks like a fungus. A close inspection will tell you if is a leaching type pod. You will be able to see it. If it looks sorts like cotton it's fungus.

Most fungal infections are fairly easy to treat. You can just add a saltwater fish fungicide (which you can find at your LFS, NON COPPER) to the tank water and hope for the best, but a more thorough procedure will greatly improve the odds of a cure as well as prevent another outbreak.

Remove the fish to a QT (five gallon bucket with ro/di, salted and buffered to tank water, as well as same temp). Perform a thorough tank cleaning, including vacuuming the substrate and water change. Add a dose of fungicide from your LFS. Remove the infected fish from the QT and place it on a soft towel soaked in saltwater. Cover the fish's eyes with a corner of the towel to reduce struggling. With a dry paper towel, carefully scrape the fungus from the fish. Wet a cotton swab with tincture of iodine or Lugal's solution ( I prefer the lugal's) and daub the infected area until covered. Let the solution sink in for a few seconds then return the fish to the tank not the QT water. Add a pump and stone to the QT while you work on the fish.

If you go this route don't use the prime. It's a good idea to have a small 2.5 oz bottle on hand for emergancys.

You also need to clean the filters in that canister more frequent.

Get some pods and build up your population as well they will help keep the pollutants down.