when i started the hobby a few months ago, i am using shoplights over my 60 gallon and the plants did pretty well. The only plant that struggle is the Rotala Macrandra where i do not get the full redness of the plants.
i used a total of 3 shoplights - i got 2 free fixtures and bought one for $6.99 at Home Depot. Each shoplight i put in x 2 qty of 6700K T12 40 watts (also from Home Depot $5.99 for 2). So, for less than $30, i got 240 watts over my 60 gallon. I am sure that Home Depot will have the 6700K for your 20 gallon requirements and you only need to get x 2 of the 40 watts.
Had just upgraded my lighting to a 4 x 55 watts AH Supply Bright kit and definitely no regrets on this lighting upgrade.
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