Plecos should never live on just algea. They should be eating veggies such as cucumbers, kale, spinich, and collard greens on a regular basis. If you want to give them a treat then throw in an algea waffer but they usally perfer the real food to algea anyway.
You'd be better off supplementing your plecos with healthy alternatives.
This is a case of be careful of what you wish for, you might just get it. Spend too much time trying for algae, you might end up with all sorts of it you can't get rid of.
my plan is to grow it in a seperate tank on the stones and change them every now and then. i do feed my plecos heaps of other foods. I just thought the look of the algae would look cool and bring the plecs out more.