If you are sure that it is algae and not mold, then it probably won't bother him. If it is mold, then it needs to be removed and cleaned because mold can cause irritation, release spores, and cause various other problems (not to mention smelling pretty bad).

If you want to keep the box but reduce mold/algae growth, switch the substrate to cypress mulch instead of moss. The wood naturally reduces mold growth and smells nice for weeks. It holds moisture well too.
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Lincoln, NE
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