Anything I can do to save this poor guy?

[joltz]

I have a 20gallon fresh water tank. I perform a 20-25% water change every week, change my charcoal bag in the filter every month and on every water change i always check PH, ammonia levels, treat the water etc etc.
Ive never had a problem performing a water change before.

So today as im doing my water change, my upside down catfish (not sure of its proper name) starts floating up top all limp and his head basically goes up against his tail, throughout the whole water change he stayed like this but I could see his fins moving very fast, (he was fine before this, or seemed like it anyway).
Once i finished the water change i kept my eye on him and he started to recover, he started swimming slowly and seeked seclusion by a near by plant where he stayed there for a while, my suckling cat fish then attacked him and he seeked refuge by the filter, i seperated the suckling cat fish and moved him into a section i have closed off in the tank so he wont harrass him.

But since then he looks weak, he doesnt seem to want to swim and I think hes going to die, this is my favourite fish in the tank, ive had him for over a year. Hes now been hiding in a little boat i have in the tank and he refuses to come out, im thinking he went into shock maybe?

Any advice what I can do to try and save him?
All other fish seem fine since the water change.

Thanks for any help.

 

[skimpy]

Did you put in the dechlorinator (I know you've been doing this a year but it's easy to get distracted so just checking).

Have you done a test on your tank water since the water change?

Have you done a test on your tap water?

If not try this and see if anything show up, let us know readings

EDIT: Did he get knocked about when cleaning

 

[joltz]

Should have added these when I wrote the initial message.
Did the water change at 6pm, 1.30am now so i have to remember these off the top of my head, might be abit off here.


PH - 7.0 - 6.5?
Ammonia - NIL
Nitrite - NIL
Nitrate - 10ish? (think thats minimum, either that or im doing the test wrong)
Temperature - 28C
Didnt do a test on water hardness, not sure what Sydney tap water is like.