GSA loves bright tanks. Are you using CO2 and fertilizers? With that much light you need them.
I found out that adding more than the suggested amount of phosphate either makes the GSA grow soft enough that the otos and ramshorn snails can eat it or discourages it.
Rosy barbs love it, when I popped it off the glass with a razor blade they scrambled to get it. Their mouths are the wrong shape to be able to eat it off surfaces though. Credit cards can pop it off too and they are safer to use.
Otos and snails like the taste of it but it is pretty tough stuff to eat. One time I saw a tiny ramshorn return again and again to a small amazon sword leaf covered with GSA and after a few days the poor leave hadn't any algae on it but it was severely damaged by the rasping of the snail.
It also dies if exposed to air and my tank got quite the water line after water changes.