Sorry to hear of the loss Martin/George. having kept aros for a good part of 40 years i am still at a loss as to why it should just drop off just like that as they are incredibly hardy fish and can withstand variations of water conditions. Don't give up Martin.
This aro has been with it's previous owner for nearly 3 years raised in a small tank on it's own in very, very soft water at a ph 6.4 and my tank is about 4 times the size with many other fish, very hard water and a ph of 7.2. Thrashed about a lot when the guy caught it but felt with such a hardy fish as hp points out that with slow acclimatisation and good quality water it would not be a problem. I guess i was wrong. When it entered the tank it seemed very lethargic and spent it's time sitting normally near the surface but with very little movement altho not breathing heavily and so I felt that once he settled he'd be fine. Woke up this morning and he was exactly where he was when i went to be except upside down. I am devastated. A dream fish gone.
RIP my super red. You were amazing. If only for 1 day.