We have had our tank set up for a while now and it is fully cycled. We test our water regularly and have had no changes recently, everything is at a satisfactory level. We have one concern, lately we have noticed a black discoloration on all of our artificial plants. I am not sure if this is a mold or something. It doesn't seem to be algae. We have tried to scrub it off when we do a
water change in the old tank water but that doesn't do anything to remove it. It is getting worse and I don't want it to take over. Do you know what it is and what we can do about it?