Anyone can agree that having a tank wiped out by disease is a terrible experience and having to treat a reef system for ich or marine velvet is a lot of frustrating work. The best thing a hobbyist can do is avoid the issue from the start.
There are generally two ways of treatment for an infected fish: freshwater dipping and putting the fish in quarantine. Dipping is to be used as part of a treatment and is not to be used as the primary treatment or solution. Quarantine is effective on its own, but dipping can increase the rate of succession. It is best to know how to do both methods.
Quarantine Treatment
By putting your fish in quarantine, you are effectively preventing your saltwater aquarium or reef tank from getting any diseases the fish could 
potentially have and treating the fish for any diseases it could have. It can be used to prevent diseases or to treat an already infected fish.
Quarantine is also used to observe the fish for feeding habits, behavioral traits, and overall health.
Quarantine works by isolating a fish from the main display tank to stop diseases from spreading to other fish. It is a whole separate system, only set up to be a quarantine tank. It is not connected to the main display in any way. Without having any rocks and deep caves, it is much easier to net out a fish that need to be taken out of the tank. Quarantine tanks have a basic filtration system and some media within the tank to provide surface area for beneficial bacteria. Some even put sand in their quarantine setups, but I recommend not doing this.
During this time, the fish can be observed and treated for any diseases it has. The hobbyist can see how and what the fish eats. They can see if the fish is a coral eater or if the fish has a strange behavior of rubbing itself against the sand. If any issues with the fish are found, they can be researched and treated accordingly.
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Some people in the aquarium hobby may argue that quarantine is not necessary. They may say you can simply just dip or feed garlic or do some other “kind of works” method. In reality, these are just ways for lazy hobbyist to feel they are doing something about issues in their tank. If you want to be successful with your saltwater aquarium or a reef tank, you need to be productive in doing what is necessary to benefit your tank. This includes using a quarantine system. If you do not use a quarantine system, you are prone to have a fish with a disease to cause your whole tank to become infected or you may add a fish that does not eat the food you feed and now it is much harder to train that fish or take it back. Also, by being indolent with your quarantine system, you are essentially causing more strenuous work for yourself as a result. I can assure you that if you do not put your fish through quarantine before it goes into your display tank, you will regret it. It is better to take the advice in this article then find out by going through the tribulations for yourself.
Setting up a quarantine system is fairly simple. Find a tank that is a suitable size for most common saltwater fish to live in for up to five weeks, which would be anywhere from 20 to 75 gallons. The tank can be simple; it does not have to be nice. After you have a tank, you will need to decide a form of filtration to use. Generally, any kind of filtration will work. Most commonly hang on filters are used, which are fine. Additional media such as foam blocks or bio balls can be added to provide more surface area for beneficial bacteria. You may also want some kind of powerhead for water movement in the tank. A light can also be used to allow the fish to adjust to the aquarium day/night cycle but is not required. Lastly, you will want some sort of object to provide hiding spots for the fish to reduce stress. Big pieces and plumbing parts are typically used and work well. Avoid using live rock or any rock because it is known to soak up medication. Now, set up your tank and begin cycling it. You will need to do water changes; your goal is to keep the ammonia levels in the tank low. At this point, your tank should be ready for fish. Fish are most commonly put in quarantine for four weeks, but it depends on what is observed during quarantine. Observe your fish during for at least four weeks and research any results you find to determine treatment solutions.
Dip Method
The dip method is a treatment for parasitic fish diseases in which the fish is put into freshwater for several minutes. It is a method used as a pre-quarantine treatment and is not used on its own
to get rid of diseases. It can also be used during the quarantine process as a treatment to better fight off the disease.
Unlike invertebrates, marine fish are able to survive in water with decreased salinity levels for some amounts of time. Dipping works in this way by putting a marine fish in freshwater, which it
can survive in, to kill off parasites that are unable to handle the large reduction in salinity. This is not to say freshwater dipping does not cause stress to marine fish, as marine fish will become stressed and show signs of stress. They can only be in freshwater for certain amounts of time and will die if they are in for too long.
While quarantine is completely required to treat saltwater fish for diseases, dipping is not. It is not required, but it will greatly increase the chance of your fish surviving the disease. It is an extra step hobbyist can take to better ensure the survival of their new fish. When it comes to the reefing hobby, most people will agree that those extra steps are well worth it. It is simple and easy to do. So, why would you not do it?
To dip a fish you first need a container to put the fish in. A one-gallon bucket will work for single fish, but if you are looking to dip multiple fish, a five-gallon bucket will be more suitable. You will then need RO/DI or dechlorinated tap water to fill the container with. The water needs to have temperature and Ph level the same or somewhat near to the water that the fish is coming from. You may find that the RO/DI water is too low in Ph. In this case, it will be better to use dechlorinated tap water because it generally has raised Ph levels. It is very important to match the temperature and Ph of the water to reduce the stress of the fish and to have more successful results. You will also need an airstone to put in the container to keep the water agitated during the process. Now, simply put the fish into the freshwater and observe it or them closely. It is common to see the fish breathing heavily or rested on its side. They should be in the freshwater for about five minutes, but some fish may need to be removed earlier if they show extreme signs of stress.
Use the quarantine process to guarantee your display tank will not get any diseases your new fish have and to treat your new fish for any diseases they do have. Use dipping in addition to that to increase the chance of an infected fish surviving a disease and to simply further treat it.
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