Mulm all over driftwood? Green algae all over Apisto cave?

[KyleKVK]

My water went from crystal clear to looking 'dusty', I think my filter needs cleaning!

 

The big piece of driftwood in my tank has a film of mulm on it now. I know this is good for plants, so I'm thinking of just leaving it, but my plants aren't near my wood, so I'm torn.

 

I also have an Apisto cave that my male used to guard, but ever since it's gotten covered in algae he doesn't go near it. Similarly, the female doesn't hide in there anymore. Water parameters are fine, but this slight change in behavior makes me curious. Should I bother cleaning it? It's a little unsightly but it ultimately isn't doing any harm, at least harm that I can see.

[CanadaAmanda]

The mulm would indicate not enough mechanical filtration and/or not enough flow in that area.... definitely clean the filter to see if that fixes it, a gunked up filter can run way slower than a clean one.