The only time I've ever had green water is in dirt tanks too. I tried all the above to get rid of it(flow rates, co2, lighting levels etc.) the only surefire cure I've found is to use a diatom filter which clears it in an hour or less. You can try to do a blackout but it didn't work for me... the plants will suffer and give algae the edge as soon as the lights are back. Gw is resilient and doesn't seem to "run its course" unfortunately. I've heard uv sterilizes work too but never tried it.