We can give you some short-term corrections, such as a single dose of 1ml / gal of Excel, to knock it down, but the best way to reduce and contain it is a longer-term approach, which involves having the right light, for your situation, in order to establish healthy plants.
If you provide as much of the following info as possible, then we can better advise you:
- Light (make & model): ideally, PAR and PUR reading at the substrate and photoperiod?
- CO2 setup (if any) and, if you inject CO2, what is the CO2 ppm level and how is it measured?
- Current NO3, PO4, GH, KH, pH and TDS readings?
- What you are dosing (product and quantity) and how often?
- Substrate type and how long has it been in place?
- What is your filter setup?
- Cleaning regimen (filter and water change frequency and amount)?
- Circulation: surface rippling and are all plants gently moving from top to bottom?
- What is your water source and do you use a water softener?