Mold Patches in Filter Walls

[Melfice]

I check my filters at least once a week (inside) and there will be patches of mold (I think) on the water line inside the filter. Is this normal? I take a clean piece of paper towel and wipe it. The tank and the fish are fine tho. There is no build up's that I can see. Or maybe there is something wrong with my water? All tests are fine for Ammo/Nitrites/Nitrates etc. Any feedback will help

P.S. 20 gallon tank running for 2.5 months now. Also, I have a Bio Wheel Power Filter Pegiun 125.

 

[jams.alaskan]

Could the mold actually be colony of the bacteria that you are wanting to develop?

ALASKA

 

[Tropjunky]

well i have that too and as far as i can tell it does nothing to harm fish i think its baceria and thats the good kind

 

[justupgraded15]

Actually, they are calcium deposits, same thing happens to a swimming pool. Just wipe it off when you check you filter. It will not hurt the fish unless you let it build up for a really long time and it all falls into the tank.
J.R.