I think it's a phosphorus deficiency, but wanted to get some more opinions. This is either a red melon sword or red flame sword. I feed with root tabs every 3 months (it's time for more) and all in one liquid Fert (easy green) 3 times a week. My nitrates stay around 5ppm so maybe it's nitrogen? Everything else looks pretty good...been battling a little green hair algae near the water surface on pogostemon octopus and windelov, and GSA on some anubias and Scarlett temple. Thanks for any help!