brown dirt on glass

[Johnb123]

once scraped off can the live rock and skimmer filter this or does it need to be removed mechanically with a filter sock or sponge?

 

[CyclistMT]

These are likely diatoms (a type of algae). Some of the critters in our tanks will consume them as you scrape them off. Probably would not be exported via a filter sock (as they are very small) but a skimmer will pick some of them up. Overall they are not really a bad thing but if you're scraping often it could indicate increased nutrients (especially silicates if you're not using RO/DI). If that's that case you may want to evaluate husbandry practices to avoid other nuisance algae from showing up or get an RO/DI for top off if you don't have one.

 

[CStrickland]

Depends on the sock. Some are more fine than others, vendors will list the microns to let you know. Maybe a large mesh wouldn't catch it but the fuzzy ones do for sure. I make my socks out of cheap felt from Walmart and they caught a ton of diatoms. Often this issue goes away on its own after a while because they need silica like cyclist said. That can come in as part of the rocks and sand you set the tank up with, and run out after a month or so. I think it goes faster with a filter sock catching them because of you take the dead ones out of the tank then they aren't rotting and releasing that silica back into the water for more diatoms to use. But that's just a theory, I don't think anybody has done it both ways to see for sure.

It's annoying but it goes away on its own if you use good water.

 

[Johnb123]

diatom really harmful to fish? could i have made them really sick from this?

 

[CStrickland]

No.
Why would you worry about that?
Are your fish sick?

 

[DubiousMaximus]

There are mesh types used specifically for diatoms. Swimming pool filters use diatom shells as filter media (DE Filters) uses mesh over several grid like ribs to collect algae and fine particles. Though I would not recommend a DE filter for a reef tank

Best options are snails, regular water changes and skimming them out.

 

[Johnb123]

but live rock can't consume it over time on it's own right? it must be eaten by snails or mechanically taken out?