The quarantine tank procedure I use is:
When I add new fish to my quarantine tank I leave them in there for 1 full month, I do a water change every 3 days, and When I feed the fish I soak there food in garlic. I do this for the whole month
If at any point during the time the fish are in quarantine there is a disease.
I well immediately take action to cure the disease, when the fish are fully cleared from the disease I well reset the amount of time for the fish in the quarantine tank back to a month.
So if the fish have been in the quarantine tank for 10 days and on the 11th day one of the fish catch a disease, I will medicate and cure the disease, and after the disease has cleared I well reset the time for my fish to 1 day instead of continuing to count the days from where I left off and also not counting days while the fish are sick. I we'll have to wait another month free of any disease before I can add the fish to my aquarium. If there is another disease throughout that time I we'll treat cure and reset the time again to 1.
When it is the last week for the fish in quarantine I well do a water change in the quarantine tank and also the tank the fish in quarantine well be going into.
To refill the quarantine tank I use the water I syphoned out from the main tank and I refill my main tank using tap water the same way I would refill it when I do my weekly maintenance. When you syphon out the water from the main tank just syphon out the water do not gravel vac the aquarium.
After the water change is done I wait 3 days and do the same thing again and then wait a couple more days to add the fish to the main tank
I have never had any diseases using this method with any fish throughout the whole month
The garlic and the biweekly water changes help neutralize the diseases present before they become large and strong enough to have an effect on your fish and large enough to the point were you can see the disease on your fish. This is a natural way of curing some of the diseases that you cannot see without using any meds.
Garlic also helps boost the immune system of the fish and also trigger the fish to want to eat. Some fish that are stressed will not want to eat
The reason I use water from the main tank to refill my quarantine tank is so that the fish can already start to get used to the water they will be going into before they go into that water and it we'll be less of a shock to them.
It is best to try and make your parameters from your quarantine tank as close as possible to the parameters of the tank the fish will be going into to limit the chances of the new fish from being shocked when added to the aquarium.
Hope everything goes well!