Q. I have a 10-gallon tank with five platies, three neon black tetras, two suckermouth catfish and a golden Inca snail. The problem is the green spots that cover the sides of my tank. The spots cannot be removed by scrubbing, nor do algae removers help. What is this, and what can I do to remove this unsightly problem from my aquarium?

A. Sight unseen, and not knowing what you mean by algae removers, my only guess would be that your green spots are a very hard and resistant strain of green algae that has gotten into pits in the aquarium glass. You can try removing the spots from the aquarium glass with a razor blade (or use a paint scraper to avoid getting cut). Do not use a blade if you have a plexiglas tank. If the razor blade is not acceptable, there is always the "last resort" (better known as chlorine bleach).

Remove everything from the tank, sponge the glass down with a mixture of 1 cup of bleach in 1 gallon of water, and wait for one hour. Thoroughly rinse the tank with fresh water until no chlorine smell is discernible, or sponge out the tank with a chlorine neutralizer such as sodium thiosulfate (the most common ingredient in bottled chlorine removers) dissolved in warm water. Give a final rinse with hot water (but not boiling water). Do not use hot water unless the aquarium is already warm or the glass might crack.

Next, re-set up your aquarium. You are lucky that you only have a 10-gallon aquarium, which is a very manageable size. The above procedure is also used on larger tanks, but the increased tank size plus the fish and larger water volume make this much more difficult to handle. Once the tank is cleaned, I would recommend that you increase the frequency of your glass cleaning efforts to prevent this from happening again.