The Guppy keeper should remember that many diseases and parasites can simply be avoided with proper care and maintenance of the Guppy tank. Regular non-stressful water changes, warm and alkaline water conditions, and a proper diet should keep the Guppy healthy and strong. New fish should always be quarantined in a separate tank for a month to see if it has any parasites or infections before being released among your other fish.
Sometimes Guppies seem to die soon after purchase with no apparent cause. When a Guppy is either shipped to you or you have bought it from a store, it has undergone a stressful change that shortens its normal lifespan. A Guppy bought at a pet store has undergone 10 times the stress than a Guppy bought straight from an independent breeder has. Never purchase a Guppy that has just been shipped to the store; ask that your choice is separated from the rest and put into a separate tank for 1 week. After that time, if the fish still looks healthy, bright and colourful, and active with no fraying fins or strange movements, it is safe to take it home. Patience is a virtue!
When you take your new acquisition home, remember again: patience! Open the bag and float it in the water. Secure it to the side of the tank with a clip away from lights or the heater. Add a small amount of water from the tank into the bag, and let sit for 10 minutes. Then remove some water from the bag, pouring it down the sink-- NOT into the tank and add some more water from the tank to the bag. Continue this process every 15 minutes or so until all the water from the bag is tank water, and let the fish swim out on its own. This is the only proper way to acclimatize new fish, and it should take almost an hour.
Some Guppies will be used to a salted environment, particularly those that come from breeders, and if you are spending a lot of money on such quality fish, you should consult with the breeder and see if he uses salt; if he does and you do not, you can have a lot of trouble keeping his fish alive. A fish going from a non-salted tank to a salted tank is fine, but a fish used to a brackish tank should remain in such an environment.