MacFan

I was cleaning a filter today and discovered something I've never encountered. A crystaline, almost coral-like growth inside the filter. It was at the top, and appeared to grow through the sponge to the media below. I rinsed most of it off but there is still some there. This filter has that high end media in it and it came with little balls of bacteria to put in there, so I thought maybe it was related to that, but there are still balls at the bottom and they show no evidence of this. I've not seen it elsewhere in my tanks, though to be fair, I run with minimal sponge and mostly bio media and very rarely open the filters. Any thoughts?

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mistergreen

freshwater sponge, likely.

MacFan

Apparently it's Bryozoan, which is actually an animal!? The picture on this page is the same thing, though I don't find other pictures online that look like it, though many are closer up.

https://goliadfarms.com/a-bryozoan-l...e-greenhouses/