How to control algae on the shell of an apple snail?

My son has an apple snail in his aquarium and its shell has quite a bit of algae growing on it. Is this normal? Is there a way to control it?

In general green algae means too much light or nitrate and brown algae is either too little light or an end of cycling bloom. Either way just take and wipe the shell with a paper towel. Do you have algae anywhere else in the aquarium? What color is it? I have found this site helpful in determining what kind of algae I had in the past. Then I was able to adjust the condition of the tank.http://www.aquaticscape.com/articles/algae.htm