The lights here is the key for you and since you don't have live plants you can limit the duration as much as you need to control the algae. If the current pattern you have works then great but if not then lower the time more. The algae that's there can survive off of nutrients in the water so make sure to keep up on maintenance. Another thing you can do is take all the fake plants out/decor and clean all the aglae off and put then back in. Use the same current light duration and see if it comes back. If you start to see it then lower the duration some.