So you've been medicating the tank without a mature filter? Ah. Right. You need a bottle of ammonia remover as soon as a spare second presents itself to keep the toxins away from the fish, especially while you're medicating for whitespot. Sorry, I was under the impression the tank had a mature filter.
Yes, I would put both fish in the 72 litre. The comet will almost certainly die in an unfiltered 4.4 litre tank, even without the whitespot, because of water quality problems.
If you're sure you've got whitespot, then I would treat the 72 litre for whitespot.
The problem with the 72 litre is that you've got no mature filter in there, so you will probably get water quality problems. You cannot do large water changes to help with the water quality problems (because you will dilute the whitespot treatment if you do) and you cannot add an ammonia and nitrite absorbing resin like Nitra-Zorb because it will remove the whitespot medication. All I can think you can do is use an ammonia detoxifier to lock up ammonia, and hope that the whitespot course of treatment is finished before you start to get nitrite. If not, you can use salt to off-set the harmful effects of nitrite, but read up on it before doing it, as inaccurate dosing could cause more problems.
I don't know about other manufacturers' ammonia-removing products, but API's Ammo-Lock is safe to use with medications.
Ooo, yes, good thought. I'd forgotten that Prime is supposed to help with nitrite as well. I am personally a bit sceptical as to how it can 'bind' nitrite and nitrate (ammonia is different) but as you can see from my sig I am obviously not impartial here. Worth a try I think.
Im very wary of putting the sick fish into the 72L as I think the fish in there will become sick to? Ive been treating audi with protozin for 5 days now in the 4.4l tank and there is no change.
I appreciate the advice its great but im still stuck to what exaclty I should do. So far what I think is that:
1) I should add the sick fish back into the 72L tank (but then theres a chance the other fish might become ill) 2) Buy prime and add it to the 72L tank 3) remove the filter as it will clear the medicine away 4) start treating with protozin
Is the basically the course of action I should take?
There was always a chance that the fish in the 72ltr would have caught the whitespot too as both fish were in the same tank before you noticed it on Audi. 4.4ltrs is tiny and if that tank has carbon in the filter, you might as well be pouring the Protozin down the sink, for all the good it'll do. That's probably why you haven't seen any improvement.
You don't need to take the filter out of the tank - just the carbon/zeolite part of the filter - and that shouldn't be in the tank full-term anyway.