Adding Hydroton to top of another media

[Jeff S]

My GB is only half full (about 6") of growstones. The top layer is covered with what appears to be black algae or really dark green algae. I am going to finish filling the bed with Hydroton. Can I just add the Hydroton or do I need to remove the surface layer of stones first?

[Alex Veidel]

If you cover it up, the algae should just die from lack of light. You might have a little extra ammonia temporarily appearing in your system, but I don't think it'll be a problem.