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Sorry mate still dealing with cyclone issues here only just saw the tag - as Winston said sounds like swim bladder unlikely to 'heal' in the sense that it will revert back to normal swimming position. Have you added small amount of salt?

pm sent mate

Aggression: Aulonocara, Ottopharynx and Protomelas go straight for the eyes. They'll likely keep attacking the eye too. Yes Tri-Sulpha would help but not if the other fish keep picking on it.. Sometimes they'll lose the eye and be ok other times they will die. Tri-sulpha and salt in a quarantine tank would be a good option. Don't think I'd bother with TS in main tank though. If your only option is leaving in main tank I'd add salt but expect to lose the fish.

As well as your heater you answered your own question in initial post - they don't like the intensity of your lighting..

No insurance on perishables - sent entirely at senders risk

As @Lictoga identified these are a species that live in massive communities in the wild. Small juveniles can school in the thousands - as they get bigger they have more territory to themselves but still live in close proximity to others. The light substrate is not ideal and the tank is too bright for them. They like a lot of driftwood - smaller pieces they can get into and under and a med brown gravel is better for their colour.

All Mudskipper spp., will do that. King Mudskippers (N.T) are very expensive and rarely available as the freight is very high, and not enough interest in them to justify breeding. Need a massive tank too - can get bigger than 45

Many choices - Empire Gudgeons, Ambassis Glass Fish / Glassy Perchlets, Hardyheads. If you want to do your bit to help an endangered species Honey Blue Eyes are an option - they are protected and can't be bought or sold however there are members on here in Bris that breed and may give you some. Another fish to consider Rhadinocentrus ornatus - only a matter of time before they too become endangered - some populations already wiped out. Don't catch in the wild - plenty of locally bred fish in SEQ. Just put one species per pond if using either of the latter.

celebese Rainbows are not native

Mudskippers are way more entertaining - way more colourful and are bred here and readily available

Good advice above. The lack of oxygen is the issue when tanks get hot. Make sure you have additional aeration. Water changes are the first thing I'd do regardless - yes they should reduce your water temp but also will improve water chemistry and remove / dilute potential toxins. When you clean your filters be sure to do so in tank water - not tap water - or if using tap water add neutraliser first.

Whilst I agree with the above - shape is off for a brasiliensis - I'd like to see other photos as based on that one pic - I'd be inclined to say hybrid Brazil x ? Head hump and mouth are wrong too. May be riviulatus x but I can almost see Red Hump in there.. is it just me?

Do a waterchange, add salt. Bacterial infections often inflict goldfish when the temp gets hot. Increase aeration. I'd recommend treating it with a broad spectrum anti-bacterial treatment available from any aquarium shop.

Hi mate - honestly - from remembering the basics of your earlier posts - and with the above in mind - I would say that the fish are indeed most likely the issue. I would never advise buying new fish and putting them in without quarantining for a minimum (absolute minimum of 4weeks - ideally 6 -8 weeks though). With the Peacocks you don't really have an effective "control" to test the theory as you don't know what if any diseases they may be carrying. You probably wont want to hear this but if it were my tank - I'd chlorinate and start again.