Qt, qt!!! LESSONED LEARNED
Hi, I do not have a question so no need to reply to this. I just wanted to post my experience so that others can see it CAN HAPPEN TO YOU! 
I am battling ich, a severe case in my 29 . I have held the ich in my 55 at bay, minimizing the outbreak with constant water changes and dips and using Paraguard. I am hoping to continue this until my 125 is close to ready, then get out the copper or Quick Cure [ clowns sensitive to CopperSafe? Although she has showed no symptoms]. 
I have too many fish for my 20 gallon qt [ yes I have an extra tank but it surely won't happen to me!]. 
I plan to dose the 55 right before I move them then I have time to move the 55 in the basement cycle it, place the fish in the 29 in the 55 an then I have another qt tank. I have spent so much$$$ I don't want to buy another tank, [ unless I get a severe out break in the 55, then I will] my husband would kill.  I have a 55, a125 [cycling] and a 20 qt waiting for future arrivals. Looks like the Shedd Aquarium in my family room. 
Okay enough of the rambling. 
I dipped my fish from the 29 in a lowered sg. w/ formalin, lowered the s.g. in their tank, still infested. I added 2 fish to my 55 - a 4 1/2 inch redheaded wrasse and a marine Betta [ someone told me they are parasite resistant ha!!].  Wrasse was in a friend's tank, no qt of course. I had a flame angel at the time I have had for 6 weeks, I had attempted 2 before [ one eibli who died in 3 days, never buy a dark gray eibli]. The other angel also mysteriously died after 2 weeks so I was so happy to have this one doing so well. Until I had removed a royal Gramma to the 29 because it had spots and removed all substrate and added live sand. 
All was fine till I added the wrasse and Betta both within a couple days of each other. The flame angel was brutal with the wrasse but the I think the Betta intimidated her [ even though she would still come by and flip her tailfin in its face then swim away. A day or 2 after adding the Betta the flame had white spots [ by the way , I did qt the angel for 2 weeks and F/W dipped her in Methylene blue prior to adding her to the 55]. 
I removed the rock and dosed with Quick Cure [I know not to medicate the main tank but I thought putting these fish plus the small hawkfish in qt would be too stressful for all especially the wrasse]. I dosed for 2 days, the spots disappeared so I did a water change an switch to Paraguard since I was getting a slight Reading on nitrites . 
The next morn. the flame was swimming erratically darting around frantic turned on the lights ich!! She seemed to be in such distress so I removed all the fish to a F/W Methylene blue dip placed them back, the angel went to the bottom and laid there breathing heavy finally she died. As I was watching her lie there I realized I had forgotten the tap water conditioner, I have 2 small kids who were awake at the time so I was hurrying and my ignorance of qt and carelessness killed my favorite fish. 
So I want to tell all your readers that I will never put another fish into a display without a 4 week qt. I am exhausted getting up in the morn cleaning tanks and worrying about these fish, I have spent a lot of $$$$ on meds and sand and tanks and so on I have gotten behind on some bills to pay for my mistakes IT IS NOT WORTH IT!! QUARANTINE YOUR FISH!! It saves money and heartache in the Long run!!  Thanks for all your help in the past and in the future, Kimme 
Thanks for your advice. I did some more reading and I now am more confused, I also really like the Red Sea purple tang...how are they on that ich magnet scale? The LFS I shop at will trade in fish if they are not working, or years later if they get to big for the tank. So, I guess that leaves me a little leeway as far as choices. How about the purple or Kole tang and a butterfly fish? Neither get a foot long. I think I will stick to maybe 2 fish under 8 inches and no more. What would be a good butterfly for my size tank? Thanks a bunch for your help.
Kim
<Thank you for your emphatic message. Bob Fenner> 

"Quarantine? As in disease prevention? Oh, I don't have to worry about that, my dealer only sells "clean" livestock". Oh really? "Infections and parasites are not a problem with my super-duper all-bug zapper U.V. filter combo.; I just plunk those new specimens in and the system does the rest." Don't bet on it.

A separate system for observation, treatment, and "hardening" of new livestock via quarantine is not a luxury for the privileged; it is a serious working tool of all earnest marine hobbyists. Don't wait until you have "the" dire need for an "in-between" system; buy and operate a quarantine tank in tandem with your main/display set-up.

A Quarantine System:

Is a smaller version (10-50 gallons) of a total marine set-up. It generally will have the following components:

1) A chemically inert tank of glass, fiberglass/wood, acrylic, +with a complete cover; possibly but not necessarily with a light fixture. Darkening the sides is a good idea.

2) Synthetic or "real" seawater. Some folks utilize their "spare" system to house, mix/age new water. I suggest you go the other direction and siphon "water changes" into the quarantine tank, and use a trash-can arrangement for preparing and storing new water. You want water quality to approximate your main system; what better way than to start with the water from there?

3) Some source of biological filtration. A sponge, cartridge-type outside power, or canister filter is better than undergravel, wet-dry or... You want to control the water chemistry in this system with a minimum of co-interaction with decor, gravel, mass populations of micro-organisms.

4) Test kits for at least pH, ammonia, nitrite and any therapeutic agent you might be employing (e.g. copper).

5) Chemically un-reactive cover.. PVC pipe et al. that will grant your livestock some sense of physical control, but won't absorb or otherwise change water chemistry.

6) Temperature control and monitoring. A heater and thermometer.

7) Treatment chemicals, nets, miscellaneous.

8) Oh yes; also a writing utensil and recording medium. Pen and paper to keep track of what you're doing and have observed.

Procedure: A Standard Operating One

First, let's state our objective: "To treat incoming livestock in such ways as to severely reduce the likelihood of disease introduction, or a weakened specimen." Okay, sound's good to me.

1) Having studied up and purchased (a) healthy individuals, possibly a dip/bath in freshwater with or without chemical additives is executed and the new stock placed in the ready quarantine system. Any chemical "medicines" (typically copper-based) have been added and their concentration checked (and recorded) twice.

2) The livestock is carefully observed daily along with testing and adjusting for treatment concentration (if any). Unusual appearances and behavior are recorded. Feeding is light, with any non-eaten excess promptly vacuumed out.

A note here regarding sharing the same isolation system for both fishes and non-fishes (invertebrates, rock, algae). Of course you'll have to dump and clean the tank out for non-fish if you've treated the water with chemicals for fishes. Want an added hint? Utilize a chemical filtrant with non-fish additionally when quarantining.

3) A proper interval (generally a minimum of two of weeks) goes by in which the specimen shows no ill effects of transport or disease.

4) It is in turn placed through proper acclimation technique, and possibly another dip/bath as in 1) above enroute to the main system.

Advantages To Be Gained:

A) The principal scourges of marine reef fishes are virtually eliminated. Protozoans like salt water ich (Cryptocaryon), Amyloodinium (an algae to some), Glugea, Brooklynella..., bacteria, and many if not most all crustacean, worm problems are solved by this screening procedure.

B) Transit "disease" is alleviated. The jet lag some livestock goes through is greater than that some of it's owners have ever endured themselves. Given a brief respite to rest and reconstitute, new specimens are far more likely to rapidly adjust and not be bullied by existing tankmates in the main system. Very often, the animals, algae and rock at your dealers was "on the reef" just days before. Give them a rest break.

C) Non-disruption of your principal system. Think of all the time and money you have or will have into the display unit. How would you like to tear it down, completely, possibly toss the gravel, scrub and sterilize everything because of "trouble" that could have been simply avoided by quarantine? I'm talking about getting rid of infectious and parasitic diseases, treating with remedies in the main system for secondary infections after them, eliminating the reproductive products of those diseases, and dead organisms polluting your tank.

D) All the other things you can do with an extra tank. Think of the peace of mind of knowing that you have somewhere to put your livestock should the other system "go down".

Summary:

To the uninitiated, the issue of quarantine must seem like this writer's "pipe-dream". I can feel some of you through space and time thinking, "this guy's nuts; people aren't going to do this". Dear Reader, indeed, I may be bonkers, but all advanced aquarists, public aquaria and breeders of marine livestock, small and large employ quarantine to limit their losses. You should as well.

Don't wait to learn the hard way. All marine fishes and much non-fish livestock must be quarantined, regardless of how and where they are acquired.

Bibliography/Further Reading:

Anon. Quarantine your fish!. SeaScope Spring 89.

Blasiola, George. Quarantine. Marine Aquarist 7(6):76.

Campbell, Douglas. 1980. Marines: Their care and keeping. Marine aquariums made simple, part four (quarantine). FAMA 5/80.

Hare, Dennis. Care of new arrivals. Marine Aquarist 7(3):76.

Ostrow, Marshall E. 1978. The quarantine tank. TFH 5/78.

Robertson, Gloria. 1987. Quarantine methods and procedures. Marine Fish Monthly 2(9):87.

Wagner, Howard M. 1987. The adjustment tank. FAMA 10/87.