I fixed the title for you. 
#2 - is adding more phosphorous. If your dosing just add more.
I have two 16 watt over my tank. They do fine. 20w might be pushing it. You might want down your light a little. I can grow high light plants with the 16watt.
#2 - is adding more phosphorous. If your dosing just add more.
I have two 16 watt over my tank. They do fine. 20w might be pushing it. You might want down your light a little. I can grow high light plants with the 16watt.