Hey guys.
I have a 5.5 gallon betta tank. I have FLUVAL STRATUM as the substrate. I need some more. There is some BGA on the substrate. Would it be OK if i put substrate (FLUVAL STRATUM) on tp of the Blue Green Algae? Would something bad happen underneath the ne substrate? I sprayed some Hydrogen Peroxide on the patches of BGA, but still..
THANKS!

If you bury the BG algae in the substrate it will die. It has to have light to live. When it dies it will decay. That will probably not do any harm unless you have an awful lot of it buried.

Should be OK. I've had an attractive layer of cyanobacteria below the surface of the substrate against the glass ever since I've set up my tank. It's done no harm that I can tell, and it has never migrated to the tank proper (knock on wood!).