Baby sitting fish tank - fish look sick!

[momentarydiversion]

Im babysitting a tank for a few days while someone is taking a holiday - and it looks like one or two of the fish are getting sick.

Water test parameters - all good, no ammonia / nitrites (some nitrate, maybe 20/40ppm) and Ph about 7.4

The fish are harlequin rasboras, and one of them looks a white/grey kind of colouring on its body. His fins are a bit tattered, but not sure if that's because he's been bullied, got stressed, then sick, or just a symptom. They are only about 2 weeks into the tank, don't know if he's just stressed out from that.

He seems to behave alright, eats ok and swims around etc.

I've looked into ich, but it doesnt seem like there is is any of the discolouration on the fins, its body based, and only on one side of the body. Fungus?

Photos attached, but a cameraphone and little fish does not lend itself to well focused images.

I suppose main questions are

- What is it?

- What can I do about it?

Ancillary to that is how harmful is it likely to be to other occupants (other fish, some RCS and a snail) is it worth getting him into isolation (or is too late?)

Tools I've got would be

- Can do a water change

- Stress zyme and / or stress coat

- table salt (no marine salt - so this probably doesn't count)

- can isolate into a small container.

[momentarydiversion]

Ahh - another piece of the puzzle - bullying could be a more important factor above

http://www.qldaf.com/forums/general-aquarium-discussion-19/lampeye-chasing-rasbora-98613/#post657799