Black spots inside cave

[Eva]

I have been using this reptile cave in my tank. It is sort of supposed to look like a rock - I've seen others here using one, too, maybe y'all know what I mean? Anyway, I took it out today for a scrub and found these black spots on the underside. They look like mildew you can get on grout in the bathroom. They weren't there when I first bought the cave. Pic below - any ideas?

Thanks,

-Eva

[Johnny O. Farnen]

Looks like mildew to me. Safest way to get rid of it would be dry air and warm temperatures, followed by a good salt scrubbing. Finally I would seal the porous interior of the cave with a good thick coating of high gloss enamel based paint.

[Eva]

Thanks, Johnny - I didn't realize things could mildew underwater. Great, another nastiness to look out for. I think I'll just keep the cave out of the tank and use something else instead.

-Eva

[Markw]

I would keep it out of the tank too. I wouldnt risk anything hindering the water conditions in the tank. Would the paint not do this too? I didnt realize paint could be put in an aquatic tank?

Mark

[oceanblue]

It might just be water penetration through cracks in the glaze but even if it is mold it is unlikely to be harmful to tank inhabitants.

If the axolotls like the cave carry on using it. I would not try any treatments or paint.

[Johnny O. Farnen]

I would agree with Oceanblue here, however it appears to be an unglazed ceramic cave, any fungus growing on the surface could result in drastic water quality shifts.

As for paint, any water safe acrylic, epoxy based high gloss enamel, or clear urethane seal is suitable for aquatic submerged use unless it is any shade of blue or green. Blues and greens are often copper or cobalt based pigments which can lead to heavy metal toxicity in caudates.
However, I think that Blueberlin has the right idea, better to use something else.