Hospital tank is in action again - this time nursing the neon green rasbora with the slightly hump-backed spine. He started bending oddly and tipping from side-to-side, especially if in the current flow, and one eye looked slightly enlarged, so I'm treating him with eSHa 2000. I'm not entirely sure that this is the correct course of action, as he's also displaying slightly strange behaviours such as swimming in circles and chasing his own tail, seizing up in a C position, and the occasional flailing from one end of the tank to the other as though having some sort of neurological episode, albeit at least some of this seems to be connected to being spooked easily such as through any movement in the room or a light being switched on. He's one of the first of the two batches of neon greens, and they haven't fared as well as the second batch which look much healthier.
Video of aforementioned fish, an hour following third/final dosage of eSHa 2000 - https:/#/youtu.be/onfMmgtdCQ4 [remove # to watch]. Behaviour is odd, and was what was occurring in main tank prior to being moved to hospital tank. I don't think it's the same as what happened to Little Harley - his demise was very sudden - but I wouldn't rule it out altogether. He is definitely very easily spooked in the hospital tank and I'm purposefully staying away from that room to give him peace, and I'm not sure how much of this strange behaviour is exacerbated by seeing his own reflection on the bottom. It's the same filter as the fish had when in QT so, even if the flow is too strong (and I'll have another go at putting filter wool in the outflow nozzle), it oughtn't to account for this strange turning/circling. Neurological symptoms? A parasitic infection (although I'm not seeing anything)? Thoughts including course of action welcome; thanks!
Update: Have managed to reduce the filter flow with some filter sponge so that it's only a trickle and have covered the tank floor in sand. Behaviour of going round in circles is slightly calmer but still continues, including the losing-balance type of behaviour.
Further update: He seems to have calmed down a bit more. If he's still alive, I think I'll make a decision early tomorrow afternoon whether to extend the treatment course or start diluting the eSHa 2000 in prep for moving him back to the main tank later tomorrow or the following day.
Final update (first thing the following morning): Well-and-truly dead, looking as though he may have died late last night.
He had looked a lot calmer throughout the eve, and my hopes were rising that he would pull through but it seems to be yet another case of animals/humans perking up from serious illness before a sudden fatal demise. After a bit of googling, I did wonder if it might be whirling disease...