It would be helpful to get others' views on this.
In my main tank, I have 3 remaining male x-ray tetras from the original shoal of 6 (age 4), all 6 of the original shoal of harlequin rasboras (age 3.5), and 4 of the 8 recently purchased neon green rasboras (3 months). They just don't seem to be in optimum health, despite water testing pre- water changes (1 x 40% plus 1-2 x 10% per week) and water being consistently at 0, 0, 20 for ammonia, nitrite and nitrates. Problems are as follows:
* one x-ray tetra with cloudy / cataract-like eye which culminated in a pop-eye type situation, seemed to burst, leaving a flap of film over the eye which disappeared and left the eye seeming very flat and possibly blind, but the pop-eye situation has now recurred
* another x-ray tetra which intermittently has an injured eye, possibly through sparring with the former
* a harlequin rasbora which has been getting skinnier for many weeks now and who I haven't seen eating at all - he swims towards food and mixes in the feeding frenzy but doesn't actually eat anything, even when it falls or is put in front of or beside him and even when it's the favourite of garlic-infused brineshrimp; otherwise, his behaviour is fine albeit less active
* a harlequin rasbora which seemed to have scraped itself on something, this evolved into a hole-like ulcer not dis-similar to the female x-ray tetra who had this recurringly, then healed but looks as though it may be recurring
* one neon green rasbora with a raggedy tail (slightly torn, slightly speckly but never evolving completely into a fungus or whitespot) - this fish seems to have taken command of the tank, occupying the middle 60% width of it, with anyone in her space being chased away
* one neon green rasbora with the top portion of the caudal fin missing, and only a partial bottom portion; this looks as though it's just growing back when it disappears again
* one neon green rasbora with a non-full tail (ie the upper and lower portions of the caudal fin are pointier/thinner
The x-ray tetras' problems might be accounted for by a combination of sparring and becoming older. Reluctant though I am to admit it, the harlequins' problems seem to have coincided with the neon green rasboras' arrival, whether due to reduced swimming space in the same upper echelon of the tank and/or the greens' comparatively lively behaviour +/- one green's tendency to nip. I've witnessed a few nipping episodes and I'm trying to recall whether one of these was caused by a harlequin. Last week, I had a harlequin peck me quite strongly / with intent during the main water change, then again shortly afterwards (if it was the same one); in the past, they've been inquisitive but have never bitten, let alone with force. The greens' health situation was like this pre-move from QT to established tank but has never really improved. [In contrast, in the QT, all 4 "newer" (but of the same batch) of neon green rasboras are in optimum health, with tails all intact; they seem to get on very well, with no one fish being in command or chasing the others, and generally seem very content in their QT.] Any further thoughts for likely or potential causes? The only "anomaly" I've noticed is that KH and GH seem to have been lower than usual (KH=1, GH=3), although PH remains the same at 7.5 (water company seem to artificially increase it).
I have 3 types of treatment - medication which would require moving the fish to a hospital tank and which I haven't been using (which is currently in use as a QT, though), Melafix (aka tea-tree oil which I have been using in 3-day rather than 7-day doses as I've been a bit wary due to others having problems with it) - this seems to result in temporary improvement of the various health problems above but these recur after treatment is ceased) and Easylife Voogle (which, on the few occasions I've ever used it, seems to result in the hole-like ulcer developing an almost immediate saprolegnia-type fungus before falling off and healing starting but no other visible improvement for any of the other health problems). I also have catappa / Indian almond leaves in the tank.
Thoughts on potential explanations or solutions welcome (aside from the temptation to allow the new neon greens to inhabit the QT as a permanent home given that they're doing so well in there!). Thanks.