I experience this problem too with my mopani wood in my tank. It went away with time. Also my habrosus Corydoras and nerite snails loved eating it!Set this tank up about 4 days ago, had soaked the wood for a couple weeks. Very little tannin leach, but what little there is hasn't really discolored the water.
The fungus started showing up yesterday. Used a baster to try to vacuum it off, but it's not working. I have plants attached to the wood, just tucked into natural crevices, not tied on. Is this the bad fungus, or is it the normal kind? I have snails in with the betta, and they haven't touched it. Betta is acting normal, eating very well, no signs of distress.
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I posted about it on this post:
http://aquariacentral.com/forums/showthread.php?p=2841735
Hope my experience helps you out.
Patricia
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