Algae in glass but not on rocks?

[moz71]

Can some one explain why it seems I grow algae on glass rather on rocks? More so in my sump, I have a large live rock with no algae at all from what I can see but the glass is Covered in hair algae and this longer brown strands (probably just a type of hair algae). Dt has some very minor bubble Algae but I get a pretty thick film algae on glass within 3 days after cleaning. And I have a lot of rock. I am not complaining just curious. Thanks

 

[Rogued_Reefer]

It’s probably diatoms

 

[Bret Brinkmann]

It's harder for algae to grow on top of something else living like coral, coraline e algae, or bacteria. Not impossible though. I suspect your live rock has a healthy bacteria or coraline algae on it.

 

[moz71]

It's harder for algae to grow on top of something else living like coral, coraline e algae, or bacteria. Not impossible though. I suspect your live rock has a healthy bacteria or coraline algae on it.

Makes sense, thank you., I do have healthy system. Knick on wood