Its a bit surprising that you have no nitrates as even tap water has a bit…is your test kit old or expired?
With all the water changes, its not surprising to me, there is little to no nitrate.
I have "not" had detectable nitrate readings on my tanks, in the 5 years since they have been set up here in Panama.

When I lived in Milwaukee, I would get 2 ppm readings , directly after a water changes, but that was because at the Water Works, Chloramine was used as a disinfectant but my planted sumps (as they do here) would usually eat that amount of nitrate up, in 24 hours or so.
I test natural waters here in Panama wherever I collect fish, and have yet to get a detectable reading, in the clearest, to




even in the muddiest of natural waters..
One other thing to consider is normal life span.
Natural Andinoacara pulcher, lifespan is @ 5 - 7 years.
But there is no-telling what "line breeding", with no regard for anything but the fishes "color", sacrifices in the health of man-induced process.
In nature, the gauntlet of "survival of the fittest" weeds out the weak, but in the captive bred quest for fancy colors, no such checks or balances are employed.
I must admit, I would have euthanized that fish, a long time ago.








