Melafix, Ammonia, And Corys

[Schmill]

Ok, so to start with I had one of my albino corys seeming depressed. It was slow, not moving around much, and generally seemed to have a "can't be ar$ed" attitude. I put it down to it mourning the loss of it's 'partner' a week or so ago.
Depressed Cory

However I've just been told by my wife that another cory is exhibiting similar behaviour
There are 3 of them in the tank in total, 2 of them now seeming to have this 'depressed' state.

She has also done an ammonia test for me, and it's coming up between 0 and 0.25ppm, I can't think why this is though.
I recently added a dose of API's Melafix to the tank, as originally I wasn't sure if the first cory had a bit of a nip from it's top fin, but now I don't think that is the case.

So question time:

1) Does Melafix affect Albino Cory's in some way I'm not aware of?
2) Does Melafix affect the Ammonia reading given on the tests?
3) Is it 'possible' that I now have 2 depressed cory's? (I was going to get another 3 at the weekend, but don't want to if there is something wrong with these fellas)

Any helpful hints or advice greatfully received

 

[Pleccy]

Melafix is quite strong (it smells too!) so it could affect the filter bacteria, which can cause an ammonia spike. Corydoras don't have scales but plates called scutes so they can be sensitive towards certain treatments. I would cut out the melafix unless the fish are showing signs of physical damage and carry out some largish water changes.