Quarantine tanks are something everyone in the industry recommends, and they would help lots of folks at all levels in our hobby if they were only used. Such tanks are similar to going to the gym and working out—everyone agrees it is a great idea, but very few people do it.
I realize that when hobbyists have only one small tank they are not going to set up another smaller tank to quarantine new fish. But if they have anything larger than a20-gallon tank—or if they have any marine tank—a quarantine tank is really important. For either fresh or marine it can just be a 10- to 15-gallon tank with a heater and a simple active sponge filter. A cover is a good idea and the lighting can be very low.
Have your customers keep new fish in the quarantine tank for at least two weeks before letting them into the main aquarium. Some fish folks only observe the fish while they are in quarantine, while others recommend a prophylactic treatment as well. I side with the latter group: New freshwater fish should be given three doses two days apart of Quick-Cure (formalin and malachite green). For marine fish I like to use a treatment with copper.
At some stores I have been in there is a clearly posted sign about quarantine tank use. Most of the signs note that even though the fish in the store are as healthy as possible, disease and parasites can be on a fish that will not show any symptoms. Some stores try to almost insist on it for marine fish, especially fish that are susceptible to problems, such as hippo tangs and some angelfish. Promoting the use of a quarantine tank simply makes sense, and you can convey to your customers that it is not saying in any way that the fish you sell are sick.
By the way, since I make a portion of my income by writing, I really love the English language, and I find it interesting where we get some of our words. There are a number of explanations for where the word quarantine comes from, but the one I think makes the most sense is that it goes back to the plague years in Europe during the 15th to 17th century. The word comes from the Italian “quarantena,” meaning a period of 40 days. The Venetians had ships coming to their port stay at anchor in the bay for 40 days before they would allow anyone from the ship onto the islands of Venice. I have yet to ask a medical person for the derivation of quarantine and have them know it.
Good for fish, too.