Angelfish Spinning In Circles On Side And Swimming Diagonally

So I've had this one angelfish that I bought with 5 others that was kind of the runt of the group. He always seemed a little weird and looked weird. I even thought he might be a Leopald's angelfish but I doubt it because that is very rare where I am. The concerns started when the other angelfish were eating most of the food and he didn't even try to compete for it. He just stayed the same size for months while the other got bigger and bigger. I tried spot feeding but he really only got scraps. As a result of this, he was bullied quite badly as he was much smaller than the others. One night, I looked at the tank and he was swimming really erratically and weirdly at the surface like on his side. I really thought he was going to die. So I immediately moved him out of there and into his own tank and he did really well. He got a lot bigger and his fins are really healthy and beautiful and long now. However, he still swims weirdly like spinning in circles on his side. Especially when he is stressed or he is sleeping. It's really odd but I've come to love him. He's actually my favourite fish. I named him Pirate as he has a black eye patch. I know he doesn't have swim bladder disorder because he swims perfectly well sometimes. It's almost as if he likes swimming that way ? It's so strange because I see him swimming normally and he can correct himself upright. I think it might be a genetic condition ? Though I don't know because it only seemed to develop when the bullying started ? I'm not sure what to do with him to be honest. Will I ever be able to put him in with the others ? It's kind of sad really because I think he should have been a cull. I'm glad to have him because he does bring me joy because he's such a little weirdo and has such a good personality. But I do worry about him frequently. Is there anything I can do to help him ?

I’ve also no experience with angelfish but drawing on my experience with other cichlids, it sounds like bullying and stress is the likely root cause. What can sometimes work in these situations is to remove all fish, rearrange the tank significantly and replace them, with your little one going in first. This acts to disrupt their view of hierarchies / who owns the tank etc... but with the difference in size this may not work... sorry I can’t be of more help...

It's certainly possible, and I know this very well from considerable personal and aquarist experience, that long-term movement in a different way (in this case erratic and strange swimming behaviour) can continue for a very long time beyond when the original issue might theoretically appear to have gone away / resolved, and recurs especially when not fully conscious/focused purposefully on being able to rectify or carry out the movement/action the 'proper' way. The degree to which it is evident or seemingly absent can also vary too. Aquaristically ( thought I might have invented a word here but it turns out it does exist ), I had an ailing and elderly x-ray tetra who started 'bouncing' and catapulting around the tank, particularly at night when he was asleep, but who was able to control this more during the daytime - I wouldn't discount a swimbladder disorder but it might be that your angelfish can control it better when fully conscious by adapting/moving differently in compensation.

From what you've described, I definitely think he has the best prospect of flourishing if you can continue to keep him in his own tank - sometimes the benefits of that outweigh the theoretical approach of a fish being social and ought not to live on its own.  I also had an ailing and elderly harlequin rasbora who I moved into an isolation tank and who went on to a live a further 2 months than would have been the case if I had left him in the main tank where he was clearly struggling.  (Like you, I became attached to this fish, in part due to this uniqueness.)

Another example of strange swimming behaviour is of a neon green rasbora with a very curved caudal peduncle area.  In his case, the actual cause is unknown - it might be TB (which some of the other fish possibly were suffering from including many of his shoalmates who died of spine curvatures), it might be his enjoyment of riding the filter current at an angle which has actually moulded his spine into this curved shape, it might be a genetic deformity that developed over time.

I'm not sure that you'll ever know a definitive answer to the cause of it, but I hope these examples and experiences help somewhat.

Glad to have been of help.

Yes, it would be great to get him a tank of his own, and maybe also add some smaller fish, perhaps some sedate / slow-moving fish that wouldn't stress him out by being too active and that would be sufficiently small that he wouldn't be able to eat them. What size is his body? My immediate thought is some cardinal tetras (mine tend to live in the bottom half of the tank and, touchwood, seem very peaceful towards others*), corydoras, or some harlequin rasboras (mine tended to live in the upper half of the tank). On the basis of my own experience, I wouldn't recommend x-ray tetras or neon green rasboras (x-rays would fin-nip and too active; neon green rasboras too lively/active), or cherry barbs (from what I've read although usually considered peaceful as far as barbs are concerned).

[*tetras do have teeth, though, and someone has twice taken a(n inadvertent) bite of my one remaining harlequin rasbora's tail, possibly in the food frenzy at mealtimes.]

Glad he's happy most of the time and eating well. 

The general 'rule of thumb' when choosing compatible fish is to avoid fish that would fit in the mouth of a fish, so they would need to be big.  This is generally a good source https://www.seriouslyfish.com/species/pterophyllum-scalare/ but it warns quite justifiably about other tankmates.  If you do decide to opt for tankmates, then it would be worth having a spare tank for those other fish in case you encounter problems such as disappearing fish.  I've done a google of "what fish go with angelfish" and there are some interesting comments elsewhere eg https://aquariumtidings.com/angelfish-tank-mates/ or https://mrfishkeeper.com/angelfish-tank-mates/ that may be helpful.  It's never clearcut or straightforward, though, as guppies are mentioned and I've read quite a bit recently about guppies harassing other fish, especially males if they think the other fish might be female.

Hope that helps.

Platies and swordtails are hard water fish; angelfish are soft water fish. They should not be kept together as one or other will not be happy.

If you have soft water for the angels, you need to keep to soft water fish.

Angelfish hardness range is 0 to 15 dH, but fish are better kept in the middle of their range so nearer to 7 to 9 is the best. Platies' range is 10 to 30 dH so at least 15 is best. While there is overlap, it is the top end for angels and at the lower end for platies which means they are not compatible.

Angels are really soft water fish and I would not like to keep them in hard water. Soft water fish cannot remove enough of the hardness minerals to deposits form in their bodies, particularly in the kidneys, and this shortens their lives.