alex crouvier wrote:

for a relatively small tank like a 20-gallon, you need
7 watt/gallon for high light plants and 3 to 4 watt/gallon
for medium light plants

140 watts over a 20 gallon seems the very definition of "overkill". 55 Watts
from AHS illuminates a 20G pretty darn well.

Do you actually have a 20 gallon tank with 140 watts over it? Can you describe
your experience, or better yet, show us a photo?