I had tons of guppy grass in my 29 Endler tank. To thin it out I pulled up one strand at a time and simply pinched it off between my thumb and index finger. You don't have to pull it out at the roots. My guppy grass was not rooted, just floating. Strands that are only 5 or 6 inches long will survive and grow. It would be a great plant to sell or trade here at AC.
Nah, that isn't much guppy grass. Take a look at these overgrown tanks...
Pleco poop is great fertilizer. This was one of my 75's a few weeks after moving 100+ juvie BN into the tank for growout. For size reference, the little cichlids were about 2" long then:
This was the 40 gallon Endler's buffet before I thinned out the Najas and the Carapo knife thinned out the fish: