I've posted about this before. I added a lot of new sand in December. This brown scum started appearing. Posted on here and said it would go away after a few weeks or couple months. It's now the end of March and no sign of stopping. I do usual 10-15g changes in my 75g about 10-14 days. Even turn off the lights a few days a week to limit growth. Not sure what it is now or how to stop it. It really looks like crap. I clean off the top layer after every PWC. Pics showing before and after. Btw had Cyano issues before and pretty sure this is not. It used to sit on my rocks when I had it.
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