Fishkeeping - Antibiotic food - home made

I have two Oscars which are looking rather worse for wear. I recently had
my filter crash on me (somehow the multi plug pushed up against the tank
and turned the switch off) I lost two fish before I realised something was
wrong. I have completed stripped down the tank and completely cleaned out
the filter so I guess I am starting from scratch so I have a 1 kg zeolite
which removed all the excess ammonia.

The oscars (full grown) are looking light in color and the scales are
raised - not too badly but I can see black lines defining them. They
seemed to lose interest in food but have just started eating again,
although not with as much gusto as before.

I believe they are coming down with something caused by the stress of the
high ammonia and genereally less than perfect tank conditions (i had not
bee gravel vaccing for a while). I have now made the tank a bare bottom
tank to keep it ultra clean while they are recovering.

I wish to feed then an antibiotic and after googling spotted an article by
frank where he mentions baytril injectable (enrofloxacin) . I had also
read about erythromycin. My vet did bot have erythromycin but dispensed to
me 2.5ml or baytril (50mg/ml).

Question. I want to make up some oxheart feed and included the antibitoic
in this. Will the antibiotic be harmed by freezing. And what quantity
would be suitable. Basically how much of that injectable to how much food
mix. And then how much should be fed to make sure there is no over dose?

Thanks

Trev