Have you decided that you want to go ahead and quarantine your fish / inverts? Good idea! Luckily, a quarantine tank is cheap and easy to setup.
An ideal quarantine tank should be at least 20 gallons in size (75 litre), but this is dependent on what kind of animals you are quarantining. For example, for an invert-only quarantine tank, I have used a tiny Pico style 2 gallon tank without any trouble, but it did require changing the water often. If you have the space, go for a larger tank – the larger the tank, the more stable and forgiving the water parameters, and the easier the quarantine process will be.
Aside from being a decent size, your quarantine tank should have a hang on back or internal filter with sponge / foam that is already seeded from your main tank. Using used sponge media from an existing tank will help ensure that your quarantine tanks has beneficial bacteria to break down the waste generated by your tank inhabitants. Remember: keeping water parameters consistent and in range is key to the survival of your fish, especially as they are undergoing the stress of being sold and transported to a new home.
Some people keep a quarantine tank running at all times, however, this is not absolutely necessary; as long as you keep some extra filter media in your main tank you can use it in your quarantine / hospital tank. This way you can create your fully cycled quarantine tank on demand.
Other than the above, your quarantine tank should also have a heater (and/or small chiller if you live in a tropical region) to keep the temperature stable (at somewhere between 24-28 celcius or 75-85 fahrenheit).
A small clip on LED light should suffice to provide lighting unless you are quarantining corals, which would need more intense lighting. Watch out though for heat issues if using powerful lights on a smaller quarantine tank.
To keep the stress levels of your new fish to a minimum, you should also provide some PVC piping or a coffee mug to allow your new fish to hide. Should you be quarantining fish that dig or burrow in substrate (some wrasses or gobies), you should add some silica sand or other non-calcareous substrate (which is more inert) in a small bowl to allow the fish to hide. It is important that you do not use aragonite or other sands as they will absorb medications (particularly copper) making treatment difficult.
Lastly, ensure that you have the proper test kits (pH, Ammonia, Copper, dkH and Nitrate) on hand. Seachem has a handy ammonia alert to let you know when ammonia is at a critical level and a water change is needed.
Develop good habits – for a quarantine tank, test the water daily or once every two days, to ensure all parameters are within range. Perform water changes as needed (likely 50% every 2-7 days, depending on the size of your tank), to ensure water parameters are perfect – giving the best chance of survival for your new reef additions.
Now that you have your quarantine tank setup, you need to decide on how long to quarantine your fish for, and what medications (if any) you need to use on your fish.