Hi, I realized a thin film of whitish fungus on a piece of mopani wood in my tank. The wood has been submerged in water for two days prior to putting it in my tank. Water parameters are good (0 ammonia, 0 nitrite, 10-20ppm nitrate). I took the wood out and scrubbed it with a piece of coarse sponge but after a day the fungus-like stuff grows again. Is this a cause for concern for my fish? How do I get rid of the unsightly fungus?