I don't know this fish but did some searching...
There are pike cichlids and dwarf pike cichlids. While one dwarf would probably do OK in 50 gallon they are more demanding as to water conditions then the 'normal' pikes. If wanting more than 2 of these beasties you would probably want a 75 tank although you 20 gallon being a long is an advantage if not wanting more than 1.
They also want a LOT of hiding places such as wood, plants and a leaf covering over the substrate. While I don't actually know the recommendation of a leaf covering over the substrate tends to indicate that the fish likely 'digs in' and you may not see often.
With the fish wanting leaf coverage on the substrate I would think this would increase the need for tank maintenance but, again, I don't know the fish nor the tank setup that would seem to properly fit.
Sorry, I know that I'm not giving you any 'for fact' info but I wanted to relay what info I could on a quick search.