Algae-eating fish will only eat what they can, and what they want. It may not feel comfortable going near the bubbler or the heater for whatever reason. You also may have more algae in your tank than it can handle.
Even in the best of situations, algae eaters will not completely clean the tank. You will still have to roll up your sleeves and do regular cleaning on your own.
It’s also a good idea to supplement the diets of algae-eating fish with algae wafers and veggies. This ensures they are getting the nutrition they need.
Bottom line: Algae eaters eat algae but, like you and I, they only what they want, when they want. The rest of the cleaning is up to you.