I have a couple of lines of Endlers. First, they are not guppys unless they are hybreds like tiger Endlers. Don't work with hybreds as I don't believe in that sort of thing. Ok, my Endler females produce upward of 30 fry. If you isolate a group of fry in a smaller tank until they are 6 wks old you should have weeded out all the males. Leave the female juves in the small tank and feed heavy for 4 more weeks. Your females should be as large a show quality female guppy. Toss them back in or better yet, get a male from else where and put him in the small tank for two weeks. The toss them back in with mom, dad and the brothers.
If healthy, your Endlers should over run a 20H every three months and be in need of culling. I have mine in 30L tanks and they have to be thined out monthly. My Jacks and convict love them, they don't care if their culls. They are cool fish and a ten gal
with say 15 males looks really good.