Eeek! The Goldfish is dying. Can someone tell me how to save it?

[SparklyfestiveYellowFeathers]

I've kept fish all my blummin life but this has flummoxed me.
Its just one goldfish, the filter is clean, the tank is clean, the water is ok, just added more tonic and he's well fed.
For the last 2 or 3 days he looks mis-shapen and thin.
Atm he's just floating at the top of the tank breathing slowly.

Is he doomed or can I save him?

Yeah, I remember my dad feeding cucumber to the plec. It loved it.

They had a fish which I am sure had bumble or bumblebee in the name. It was very similar to plec except they loved to hide under rocks and wood and had a round belly. Also catfish like features.
Any idea what it is?

Be careful with some of the plecs and catfish they can get pretty big!

Neons are gorgeous, but tend to be quite fragile - can I recommend cardinal tetras? They tend to suffer less disease and are a bit hardier. I'd probably add fish 3 at a time, wait 2 weeks then add more.

Right, noted. Cardinal Tetras.
I think it will be a trip to another pet shop as I dont think our local shop has many tropical.

You might still find you lose 1 or 2 of each batch of fish you add, just to warn you. I seem to lose a ratio of 1 in 3 with tetras and now guppies - I don't know whether some fish are just overbred or don't travel well... My cherry barbs are pretty and suffered a fair amount of abuse on the way home (I didn't secure the bag properly and it rolled around a bit) and are still with me!!

Still, with the smaller multiple fish, I think it's easier for children to cope with the loss of one. I swear ds1 now thinks we get thrown in the bin when we die