Fish Health In My Tank

Everything crossed here @fcmf 

Update: Harley looks much improved today - pelvic fins and one of the pectoral fins completely cleared up, mouth considerably better than yesterday and able to be opened and closed properly today, leaving just the original and most inflamed pectoral fin looking still inflamed but better than over the past few days. Therefore, I think I may do a half-dose of the ordinary Day 2 and Day 3 dosage (essentially, one drop) into the QT this evening and spend tomorrow afternoon/evening gradually diluting the medication before putting him back in the main tank.

If it is the same high reading from both tap and tank water, with phosphate, my first question is did you use liquid soap to wash your test tubes? It takes a lot of rinsing to remove the phosphate residue from detergents. And it doesn't take much residue to interfere with a test.

That's interesting. I'm not sure the last time I tested my tap water for phosphate. I have soft water, with low nitrates. So if it has relatively high phosphate that would explain why I constantly struggle to get the nitrate:phosphate ratio correct.

As a further update https://#youtu.be/Hhx2oPu-Tx8 [remove # to watch], this time on the x-ray tetra with the problematic eye, the cloudy eye evolved over time into a cataract-like problem, then into popeye. The situation is deteriorating in the sense that the popeye is protruding increasingly further, with the eye considerably displaced when looking directly at both eyes together - it's as though there is a ball-bearing which can be seen when viewing the fish face-on. However, the fish is still as inquisitive and colourful as ever and with as hearty an appetite as always.

I've already tried a course of eSHa 2000 but he didn't respond well to being in the hospital tank so, especially as I'd be unsure what else to medicate with, I plan for him to see out his days in the familiar and happy environment of the main tank as it doesn't seem to be bothering him at all. With the current trajectory, though, I wouldn't be in the least surprised if either the eye completely detaches itself from the socket (if that is even possible but it might relieve what I can only imagine is considerable pressure behind the eye) or else the fish is found dead one day within the next few weeks (if the pressure extends internally).

As an update (although I'll probably jinx the situation by writing this!), the various afflicted fish seem to be doing fine. The afflicted harley seems to be much more horizontal in the tank now, without his tail drooping so much, so whatever was going on there seems to be clearing / have cleared. The pop-eyed tetra remains unaffected by his eye. I'm now reaching the stage where I'm opening the tank to do the morning feed without trepidation on account of expecting a body to be floating in the hornwort. Of course, it's usually just as I reach this stage of relative relaxation about the situation that a fatality occurs... fingers crossed that this won't be the case!

I always get the same mixed feelings at the passing of the last of a species. Good must come with the bad... but then the guilt of not feeling bad... then the excitement of new fish...   

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...

Aw, thanks @Littlefish, for your kind words.  Yes, I seem to be going through an unfortunate phase at present, possibly due to some old fish but also due to the first of the two batches of neon greens in particular not faring well for whatever reason (nothing to do with water quality which is consistently as it ought to be). Hmmm - perhaps I ought to consider a single-species tank in the future to avoid bonding too much with any one fish and also because possibly they may fare better in a large shoal...

I can usually recognise one or perhaps two individuals from a shoal but the majority all look identical to me.

There is a group of fish you could think about for the future - Boraras. These are usually wild caught which means they are less tolerant of water parameters at the edge of their normal range. You have very soft water which is perfect for these fish. Like the dwarf cories, they do best in groups of 10+ and a huge shoal could look stunning in your tank.
Chili rasboras, Boraras brigittae, are the most common, but I think a lot of shops sell the less colourful B urophthamoides as B brigittae. My favourite is the slightly larger B maculatus which is bright red.
None of the Boraras are in the fish profiles, unfortunately, but Axelrod's rasbora is in there. This fish is the same size as B maculatus and has the same requirements. In fact, this would suit your water as well but are not easy to find.