Planted Tank Guru
Join Date: May 2015
Location: Forest City ON, Canada
Getting a thick "mat" style carpet is more dependent on CO2 rather than light. I had glosso that was not carpeting very well under the lower end of high light. As soon as I started injecting CO2 it immediately starting "carpeting". Same thing with my HC, I had it under extremely high light, with no co2 and it would not carpet. The finnex light you mentioned is not the limiting factor of growing a carpet in your 3 gallon.
Flame moss (or any moss really) would look nice if you could adjust it into a mat and create a carpet effect.