Hey again so l just went to a 29 instead of the 20 gallon and again not looking to breed borellis unless they decide to so any changes to your recommendations in terms of how many and what sexesI agree with the borellii being the best choice for your 20 (tall/standard) tank and your water. One thing that I will add to the good advice given here (and this from personal experience working with the species over the years) -- once they do spawn, female borellii can be aggressive with the males. Make sure to have some thick cover in each back corner that goes to the top in addition to whatever other plants you put in there. The thicker the better. By having the plants go to the surface, a severely harassed fish can hide "up" if it cannot get any relief by hiding down near the substrate where Apistos usually hang out, and this can be enough to give you time to discover its plight and remove it. If you are doing a planted tank, you can use stem plants for this, or even group plantings of Val or Crypt. retrospiralis or similar, or taller Java Fern clumps on wood (In my low light fish room tanks, I even just use tall wood pieces in each corner or yarn mops). I would also use hardscape to provide sight breaks to divide the tank into 2-3 "rooms." Put caves (multiple) at opposite ends of the tank. I usually give 2-3 choices on each side, so that whichever the female chooses, it will not be dead center of the aquarium leaving other fish nowhere to get out of her way, including the male. Borellii are a stunning species with the benefit of being a great first-time species to work with. I don't think you'll be disappointed with the choice at all.