The only LFS here is petco and petsmart. half the time I go up there, tanks have dead fish in them. Id rather medicate them for everything upfront and the ones that survive I keep in my tank with out worry. I personally think everyone should quarantine and preemptively medicate all new fish.
I agree with the others, a 5 or 5.5 gal tank is not a good tank for qt as it's too small for most fish and definitely too small for the numbers of fish you are contemplating.
Sounds like you are aware that you are fighting an almost lost cause if your only choice for buying fish is buying from shops that routinely have bad fish.
In many cases, what they are carrying is not curable so use of a quarantine tank is definitely going to save what you do manage to get and keep that is healthy.
As for medicating, be aware that a 10 gal tank does not hold 10 gals of water. Medications that are dosed out for 10 gals means 10 gallons of water. So you have a couple of choices: 1) In a 10 gal tank, measure out 5 gals of water and cut the dosage in 1/2 so that you are treating at the proper dosage level. 2) Get a 15 gal tank and measure out 10 gallons of water so all you need to do is dose as directed on the packages.
In either case, I use a black magic marker and mark off every gallon of water so it helps me see just how much I am changing at each water change and helps me medicate properly when necessary.
Here's where I differ from most regarding a quarantine tank and hospital tank. I don't medicate in a qt tank. I use a dedicated hospital tank for medicating. (It's bare bottom and has no decor that can absorb the medications.) In a QT tank, I want to have an existing system that is cycled and running ( or can be set up quickly and have cycled filter material at the ready so it could hold life in under 24 hours. ) The QT tank should be close to a mirror image of the main tank regarding water chemistry, light and feeding schedules, etc so you can see how your new pets will adapt to that scenario. Since there are some parasites that have a life cycle of over 90 days, you should plan of having your new fish in this QT tank for at least that long ( perferably longer) to see if they break down or if they do, it can be where the fish can be returned to to heal after being medicated in the hospital tank. Blindly medicating can have as many bad effects as good so I do not suggest it at all. There are some great books out there for disease diagnosing and I would suggest having them at your disposal so that you only medicate for what the fish are suffering from vs medicating for "everything". There is an older TFH book called "Handbook of Fish Diseases" by Deiter Untergasser that has one of the easiest to follow diagnosing chart system that I highly recommend. It can be found used at a number of sites so it can be gotten at a cheaper price than new. Some of the meds it recommends are no longer available but the diagnosing charts are worth every penny you pay for the book. Once you know what you are treating, you can get what meds are available today to treat it.
Hope this helps.
