I thought I'd add my 2 cents on filamentosus. I had 2 males and 4 females in a 15 gallon tank with some plastic plants, driftwood, coconut shells, ceramic pots and a top cover of water sprite. The water was about 60ppm hardness and a pH of 3.5-4.0. Temperature around 80-82. My females were not good mothers taking frequent trips around the tank but I could always tell there was a spawn by the female showing a solid longitudinal black stripe. The male was the real aggressor guarding the area of a spawn.
The favorite place to spawn was a plastic ludwigia leaf. Every female I had spawned there. This was situated in the front corner. I had no trouble with fertility or raising the fry as long as I kept the water very acid. I did raise 40 fry in a 2.5 gallon tank for two months with lots of water changes and they grew as good as those with the parents or raised in 10 gallon tanks.