There are some other factors that should be considered here and that have not been mentioned.
First on the water change, there are reasons far more serious than nitrates for changing water, and these cannot be measured. Pheromones and allomones, urine (a tetra excretes over 30% of its body mass in urine every day), etc. Water must be changed regularly to deal with this, as these things seriously affect fish. No mention is made of the pleco size, but this fish alone would suggest more water should be changed, 50% once weekly wold be my aim.
The minimal surface are, both in terms of the water/air surface and the surface of the tank substrate, work against you in a tall tank as opposed to a longer tank. While greater water volume can help, the area is more important both for the fish's needs physically and for water quality.
Live plants impact significantly on both of the above issues (they help), and these are not mentioned.
This species, Gymnocorymbus ternetzi, is quite an active swimmer when young, but tends to slow down with age more than many other species in the characins, so that is in your favour long-term. But the tall tanks are better suited to sedate fish such as pencilfish, rasbora, etc. that are less active. These types of fish could be in significantly greater numbers in this tank than can more active fish. And always with lots of live plants, which can be very effective in such tanks.
I would not add to what you have.
Last edited by Byron; 07-03-2012 at 11:57 AM..