Cottony Algae?

Question
I have a 30 gallon tank with guppies and neon tetras.  There are also several algae eaters. All total there are around 25 fish. Two months ago the tank was cleaned and since I have a white "cotton" or spider web looking thing growing on the artificial plants and gravel and it is spreading.  It doesn't seem to be affecting the fish yet.  Filteration is a hang on filter and it has adequate water turn over.  I have never had this in over 35 years of raising fish.....Thanks.

Answer
Hi David,

It's likely mold, which is a type of fungus.  What kinds of decos are in the tank?  Have you added anything or changed anything lately?  I have heard this when people add gravel or rocks that they found somewhere and didn't clean them thouroughly enough.  It can also be from high phosphates and/or overfeeding.

What did you do when you cleaned the tank out since this seems to have kickstarted the event?  How often is the tank cleaned/gravel vacuumed/water changed?  What are the nitrate levels?  The nitrate levels would tell us if there is excess waste in the tank.

Until we know the nitrate levels I would do a good gravel vacuum, 25% partial water change and make sure the fish aren't being overfed.  Only 1-2 flakes per fish per day.  While the mold is present I would only feed every 2-3 days and see if there is an improvement.

Good luck : ) April M.