One general thing to note is that I’ve found archers to be particularly sensitive to water quality. With my old group of microlepis, I would sometimes notice some of the fish develop a slight haziness to their eyes and start to get listless if I every skimped on water changes or fed too heavily, even though all other fish in the tank seemed fine. After I moved them to a bigger tank, upped the filtration and added an auto drip system this no longer seemed to be as much of an issue.
So one thought might be that your aquarium simply wasn’t sufficiently cycled/mature. If that’s the case perhaps just give it some time and keep up the large water changes.
So one thought might be that your aquarium simply wasn’t sufficiently cycled/mature. If that’s the case perhaps just give it some time and keep up the large water changes.