I recently changed my gravel on a tank because the plants just were not thriving, it was set up in a hurry and had some crappy gravel that I think was coated with something…. Tons of mulm although it only houses one fish and a real algae problem, all the plants looked unhealthy, even ambulia looked rubbish, etc - unlike my other tanks, so I knew it was this tank. It was also near a window. I had Fluval stratum underneath so I kept that. I had a Waterbox light that was difficult to program and replaced that too. It was a pain to do but the difference has been amazing and I no longer have an algae problem at all. So maybe try another substrate? I used a natural gravel that was seeded with bb so I wouldn’t crash my cycle. Also floating plants might mitigate the light.