Another help would be a (small even) 50 dollar media reactor with phosphate remover as well. Kent phosphate sponge. Even add some carbon with it. Again you could get a hang on the back unit for space. Big water change, no nitrates, no phosphate, no light for 3 days would do wonders. But you have to prevent the root cause. Which is why I asked parimeters. If your water source contains phosphate that's a losing battle. Also raising magnesium to around 1400 temporarily helps fights algae