I'll buy a carbon filter to add to the fluval tommorrow, and some aquarium salt while I am at the garden centre. I Have put the new pump in the main tank to build up a biomass, for use in the quarantine tank, have decided there's little point in moving the 2 remaining fish to the hospital tank, as I'll have to cycle it anyway, which will mean I'll have to transfer half the water from the main tank and any bad things with it.
Catfish looks a little less stressed since the recent water change, but is definately not well. I'll see how things go, but will not bother attempting to restock for a month at least.
When I do restock, I'll buy some more tiger barbs, as they seemed to fall ill quite quickly last time, so they'll serve as a good indicator of any problems. And I'll be leaving them in quarantine for a week first.
Not put off by my disaster, my housemate has just purchased an 80 gallon tank which he intends to use for marine fish, I admire his bravery and will watch and learn with enthusiasm when he gets it running.
Cora Dora is still strong, no signs of any illness and showing good colouring, if he gets through this I have total admiration for him, that's one strong little fish.
u/d catfish I am going to try my best to help him through, he came with the tank, and I believe he's about 2 yrs old, so i feel quite guilty over my incompetence causing him to suffer like this.