There is this thick black spongy substance in my tank.. I've asked about it before on here, but didn't really have much to ask about; now the sludge has spread quite a bit in little patches over the rock; it is black and it has little air bubbles trapped on it, it is spongy, it bounces back when I poke it, it doesn't come away from the rock easily and it is definitely encrusting. It seems to grow "up" instead of "across"; like there will be tube-shaped parts of it that stick up.The clean up crew won't touch it and it seems to spread more with more light. This doesn't seem like cyano. What could it be?? Toxic ?? How to remove it??
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