Fish tank in SU - health of the fish

OK so I have a thread over in the general cold & temperature water forum about a fishtank in my SU that I've been given permission to try clean up. The tank is basically in really bad condition, and has five fish in it.

The fish are in mixed condition. The newest addition looks fine (gold comet) and apart from just being in bad condition I'm not too worried about it.

Another comet/shubunkin has a bent tail and is red all along the back - I reckon it might be septicaemia. The last comet/shub is looking OK apart from the scales look all rough and don't reflect any light.

The last two fish are a species I've never seen before. They look a bit like lionheads but don't have a growth on their heads and are a strange colour. The largest has a severely bent spine and its eyes are almost popping out of its head. It rests on the gravel for short periods then swims, and carries on with that pattern. The smaller is in terrible condition. It has a really badly bent spine, and doesn't swim - it just lies on the gravel.

As of yet I don't have any water parameters, don't know the volume (about 40G is a rough estimation), and haven't had a chance to get any photos. I am going to go in tomorrow to try get volume and photos, and will do a 10% water change. My old test kit just ran out of ammonia tester so I have to wait for the refill to come before I do them (just for ease of transport). It should arrive Tuesday.

(Edit by Kashta): Here is a link to that thread: http://www.aquariacentral.com/forums/showthread.php?t=197196

The tank is about 30G (120cm x 30 cm x 30 cm). Will add photos when I get home.

Ok so photos...

First is the full tank.
Next is largest of unidentified fish with bent spine etc. At the bottom you can see the smallest which just sits and can't swim really.
Third smallest unidentified - note the large eyes.
Fourth the worst of the two shubs/comets - you can see the red septicaemia(?), and the damaged tail at the top.
Fifth, bent spine again.
Sixth damaged tail and redness (bad pic, sorry)
Seventh is the 'less shiny' shub/comet.
Last is the relatively healthy comet.

I fed them yesterday just after doing a WC and I noticed that when they were eating off the surface, huge bubbles were coming out of their gills. I've never seen this in mine...is it normal? May be that they just swallow a lot more air than mine do...mine also get a sinking food. If it is a problem, how do I sort it out?

The little Ranchu is swimming a lot more, but I've noticed he only has one part to his tail - the other is completely missing. He'll never be able to swim properly (unless it grows back...but it looks like it never even existed) - will he still have a good quality of life provided the tank stays clear? I have some clove oil, but it really is a last resort. I could rehome him into one of my own tanks, but this isn't ideal as my housemates are starting to tire of all the tanks dotted around the place.