White Cloud Mountain Minnow Headstanding

[Kaidonni]

A few days ago, around Thursday/Friday, I noticed my old (?) male White Cloud Mountain Minnow started doing some headstanding (he's about 2 3/4 years old). So far he's only been doing it while the tank light is off in the morning; I haven't yet noticed him doing it after the tank light goes off in the evening at 9pm. I've conducted a 50% clean today and fed some mushed up de-frosted pea (I don't blanch, and the peas weren't quite completely defrosted...I mushed them up quite a bit to make sure they were okay). I normally feed flake food every other day, and try to feed pea once a week (I fed a small amount of flake yesterday after fasting on Friday - having previously fed on Wednesday - and fed the pea today, and normally I don't bother fasting as I feed every other day anyway). It remains to be seen if those make any difference, but in the meantime I thought I'd ask what it might be? An injury? Possibly internal bacteria?
 
He doesn't appear bloated, and his appetite is fine. At one stage during my 50% clean, he was actually lying on the gravel, but he soon snapped out of that and hasn't done it since. He does have a greyish/whitish growth (basically a spot) above his right eye that is decidedly not mouthrot or columnaris or viral lymphcystis or any one of plenty of other fungal, bacterial or parasitic organisms that have popped up in my searches online; it's been there for upwards of 2 months, and based on previous advice I believe it's likely to be a tumour (so it might be it's finally starting to affect him after all this time). The only thing that's new is that on the side of the growth towards the middle of his head, there's a black lining.
 
When I treated another White Cloud Mountain Minnow for a clear bacterial/fungal infection last month, the extended course of Esha 2000 - plus a second [rushed due to time constraints] course of Esha 2000 - had no effect (and very little for the other Minnow, whom I sadly had to euthanise). Whether that's because of my regular use of Prime or not is debatable - the Esha 2000 manufacturers advised me that, with my regular use of Prime, it could reduce the efficacy of their medicines.
 
Tank parameters
Ammonia 0ppm (or near enough from what I can tell with the way Nutrafin and API tests work)
Nitrite 0ppm
Nitrate ~30-35ppm
pH 7.4-7.6 (Nutrafin test difficult to read)
Total Dissolved Solids 301-305ppm
Temperature ~24C
 
Now, I realise the temperature is higher than White Cloud Mountain Minnows are meant to be in, but without the heater turned on it swings between 21C and 24C due to the effects of the tank lighting. I have actually left the heater plugged in for a good few weeks now because of previous health issues and my concerns the daily temperature swings were partly responsible (with the 'heatwave' we had, it actually went up to 26C-27C, and even with the light left off, the latch open and a fan on the tank, it made very little difference). It's been holding around 24C since the temperatures came down. I've tried different temperature settings all the way to the lowest it allows (~18C-19C), but today I decided to unplug it once more.
 
Just three White Cloud Mountain Minnows at the moment, two male and one female (what with the problems I had over a month ago, I've been taking it easy and am yet to decide if I plan to keep any more fish or not...it certainly wouldn't be more White Cloud Mountain Minnows). There is quite a bit of aggressiveness off the younger male at the moment...

 

[Kaidonni]

As a side note, all of the tests - except for Total Dissolved Solids - were conducted *before* my routine 50% clean today. The ammonia, nitrite and pH tests were conducted yesterday, the nitrate tests today - I conducted one nitrate test from a sample I took right before the clean, and a second nitrate test from a sample after the clean because I thought I mucked the original up, and they were both quite similar.
 
EDIT: Almost forgot in all my rambling...

The male Minnow in question has been rather skittish when the light has been off (at least in the morning), both with the aggressive male and when I've come close to the tank (including when I talk to the fish...yeah, I'm one of the people who speaks to his fish, perhaps a bit too loudly sometimes). He managed to get himself lodged in the canadensis up the one corner a good number of times, and on Friday I had to use a pipette to sway it about so he could swim out (I've since rid the tank of canadensis...they weren't working out, the sheddings are very annoying).
 
I have noticed a black mark/patch along the younger male Minnow's lateral line, below the very top of his body, but if these were to be ammonia burns, then based on my tests yesterday any potential ammonia spike was already over.

 

[Kaidonni]

EDIT: Took another look at the growth on the older Minnow, and I've just noticed it's slightly pinkish from the one angle...doesn't change much about what it is, though, what with the length of time it's been around.

 

[Kaidonni]

Almost forgot - Fluval 2-Plus Internal, ~50L filled. Just in case. I hate leaving details out.

 

[Kaidonni]

Another observation - the old Minnow who has been doing headstanding appears to be shaking his body and his fins at least some of the time while he does his headstanding, as if he's shivering or vibrating. He's also done it when upright - he was hanging near the surface in the top corner this morning (but not gasping for air or anything like that, just close to the surface), clamping his fins, arching his back downwards (which I've noticed he and the female do from time to time) and doing this 'shivering' of his body and fins; he proceeded to do some headstanding shortly afterwards. I did end up spooking him and he bumped into the thermometer, but not too worried about that.

Unfortunately, the temperature seems to be holding at 24C at the moment, so the ambient room temperature (it doesn't feel like 24C) must be slowing down the radiation of heat from the tank. Heater is unplugged, so no more to do about that (and this is when the light is off). Still, he is active and eating, and behaving as normally as I can see the rest of the time (except he doesn't seem to want to spar with the younger male much, he ends up being chased off quite a bit by the younger male, terrified).

 

[Kaidonni]

Took a video of where the growth is at currently. The old male Minnow is largely the same since I last posted, although he doesn't do the headstanding every day. He has been a little disinterested in feeding, but he has been eating - all three of the Minnows seem to be tearing flake food from the surface, not eating it right away, moving on to search for more flake food, and finally snatching up what they took first and didn't bother with. They ate the pea I gave them today well enough, although the old male was a bit clueless and slow at times; he even swam away for a little while, disinterested, but came back (he didn't get quite as much as the female or the younger male).
 
It looks like there is a black line along the right side of the growth (that is, looking at the Minnow head-on), and it looks quite distinct when looking at the Minnow's right side (that is, when the Minnow is facing right); it also looks like there is a slightly raised black spot/pimple from that angle, part of the black line. From the left side, that black part of the growth definitely looks like it's sticking out, and not just rounded (in the video I linked to, 0m30s to 0m32s gives a quick view of it from the left side). Not that any of this changes what it is - I do keep wondering if it's anything urgent, but as it's been there for almost three months now, that rules out a lot of possibilities (and probably just about everything one can find on the internet when looking for fish diseases - I don't know of anything that works this slowly without any major behavioural changes in the fish). Any changes now could just be normal for this kind of growth, and I did notice the black line months ago - it's just more prominent now.
 
I'd take photos, but they don't come out well, and it's extremely difficult to get a shot at the right angle.