Help - white fungal (?) growth on Rocks

Hi,

I have a 20+ gallon fresh water community tank.

I have had the same rocks and gravel in there since I started this tank
(about a year and a half ago) - and tested them with dilute acid (or
looked them up) to make sure they were safe.

Have 3 ottos, 4 zebra fish, 5 gold barbs, a large 6" catfish and a
medium Angelfish all which are healthy. I also have some live plants
(Amazon Swords and Brazilian elodea) that are doing fine. My tank has
been stable since Christmas when I added an under-gravel filter during a
major cleaning.

I have an outside AquaClear mechanical filter with Foam, Charcoal and
BioxMax cartridges. I do all routine maintenance including 1/3 water
change every month and I use Hagen Waste Control, Aquaclear and Cycle as
recomedended as well as plant food once a month.

Recnetly, I've been getting a stringy off white growth on a large rock,
some drift wood, and the surrounding gravel but noting else really. I
don't know if it is bacterial or fungal or otherwise - but it seems to
be some sort of biofilm . . . perhaps mixed in composition?

The tank seems healthy otherwise. Fish are perky and plants are fine.
Tank water is crystal clear and does not smell.


Can anyone help me identify this. Has taken about a month to build up a
bit and I'd like to know how to best treat it in case it becomes a major
problem.

Thanks,

Trev

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