Algae eating fish poo out fertilizer for more algae, and next time it could be algea that the fish dont eat. So only keep fish that you want as pets.
Many light bulbs that come with the set ups are going to be very good at growing algae. If you do not want to keep live plants, Consider changing the bulb to something other then floresent bulbs, somthing other then bright white, I use Aquaglow bulbs, they are still flouresent, but designed different. fish and decorations are more bright and natural colored, not washed out by white light, and algae growth is limited. Also, keep the on less 8 hours max if you have a lot of algae. Onestly I have very little algea since I started using these bulbs, and now i wish i had more for my new rainbow shark.