Marine ich is caused by a growth of parasites
in the aquarium. Many conditions in your fish can indicate
a case of marine ich but the most common signs to look for
are cloudy eyes, pale colored skin, cysts growing on the surface
of the fish and a loss of appetite.
If you believe that you have a parasite problem you will
need to purchase a solution from the pet store to treat it.
Ensure that the product you are buying is copper based as
they tend to work the best to alleviate parasite problems.
If after a few days you do not notice an improvement in
your fish you may need to change the water in the aquarium.
However, simply changing the water is not enough as the remaining
items in the aquarium will likely still contain the parasites.
You will need to thoroughly disinfect or replace everything
in the aquarium. If this still does not cure the problem there
is likely another infection that is bothering your fish.