Why is the fish tank got green build up in it?
I think your nitrates are too high. You said the levels are “okay” but didn’t tell us what they are. Any time your tank starts to get overgrown with algae, it’s a sure sign that you need to get the nitrate level down. You probably haven’t stayed on top of your weekly water changes. I’d start now by doing a 50% water change with same temp, dechlorinated water. Get a test kit and actually test for the nitrates, and try to keep them under 10. When you do your water changes, vacuum the gravel deeply to get the organic material up out of there, too. That’s a big contributer to too high nitrate levels, so clean it up well. I’d continue to do 20% water changes daily until you get that nitrate level down, vacuuming deeply every time you change the water. Others will tell you to put some chemicals in, or block the light, yada yada, but none of that will work if you don’t fix your water parameters. Higher nitrate levels can be tolerated by fish if they’re building up gradually, but it is hard on
