Do 2-3x a week water change, 50% etc, clean off all you can each time, turn lights off for 3 days, disconnect CO2 during this time, add Excel at full lablled rate after each water change.
You may do a daily water change+ Excel+ blackout for 3 days to really beat it back good.
However, you need to really work on CO2...........
DIY CO2+ high nuke light?
Excellent way to culture Rhizo........
You cannot induce it other ways, at least I never have after 15 years.
the only thing is, i use a short photo period anyways, and DIY co2 is with 4 bottles now.... which is yielding 3bps from my bubble counter..... and my co2 chart readings give me about 42ppm, with 6.2 PH and KH @ 40ppm
don't have a drop checker though - may invest in one over time as well as pressurized
but thanks, going to change some water again today