01-30-2013, 10:26 AM
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This is very different from wood fungus.
Wood, being an organic substance, can have any number of bacteria, fungi, etc. living in it. These can leech out when the wood is placed under water. Some may be harmless, but some are toxic. Without examination by a microbiologist, you can't say either way.
I've never seen what the photos show with rock, but as lace rock is highly porous, it is possible that some type of bacteria or fungus got into it from wherever it came from. Until you identify what this may be, it is impossible to say if it is toxic or not.
Re the UV sterilizer, that of course kills all bacteria in the water column. Are you still using it? I've no idea if this might allow something else to proliferate, since the bacteria is gone. Just a thought.