The Benefits of a Quarantine Tank


The act of using a quarantine tank is one of the most often given, and most often ignored, pieces of advice in the aquaria community. The average aquarist just doesn't want to keep a separate tank going every time they buy new fish. But it doesn't have to be as difficult as you would think.

What is a Quarantine Tank?

Some of you may be wondering what a quarantine tank is, and why would I devote an entire article to it? A quarantine tank is a smaller tank (5-10 gallons), with washable decorations (plastic, ceramic, terra cotta), subdued lighting, and (if desired) a small layer of gravel. A quarantine tank can have any type of filter, but for reasons explained later using a filter you can always put on your main tank is ideal.

The main point of having a quarantine tank is to keep the newly purchased fish separate from the other (healthy) fish in your main tank. Having the tank completely isolated with its own heater, filter, water bucket, and decorations means that there is zero chance of contaminating your tank with any little beasties that might be on your fish. These don't have to be visible, it's assumed you bought healthy looking fish, but sometimes it takes a couple weeks for a condition to show itself to the human eye.

The reason why I feel so strongly about quarantining new arrivals is that over the years I've seen firsthand the benefits of using a quarantine tank, as well as what can go wrong when it is not used.

Reasons for Quarantining

If you were to find out there is a method to keep nearly all diseases and parasites from entering your established aquarium full of beloved fish, wouldn't you want to use it? It seems very risky to take fish from the dubious tanks of the fish store, and just plop them into your main tank. I'm sure many of you have had the problem before of introducing new fish directly to your main tank, and in a matter of weeks getting an outbreak of disease or parasites in that tank which up to that point was stable and problem-free.

All the same reasons for quarantining new arrivals can also be used to help heal individual fish which have suddenly succumb to specific problems. This is appropriately called a hospital tank. If a single fish comes down with body fungus, a bad injury, or perhaps a bacteria infection, it can be placed into the smaller hospital tank, where high water quality and small medication dosages are easily obtained. However, if there's a parasite outbreak in your main tank you will have to dose the main tank. Removing the sick fish, curing them and putting them back into the main tank may just let the parasite reintroduce itself into the once-cured fish. That would be a bummer.

You do the math, using half the medication cuts your costs in half!!

Cheaper to medicate. The most practical reason for using a quarantine tank is they are usually smaller (5-10 gallons) than your main tank may be (20-200 gallons). If a parasite (like ich) breaks out in your 100 gallon tank, just imagine the costs of medicating that tank with the correct dosage of medication to rid all your fish of those ghastly things. Here's where I can say an ounce of prevention is worth a pound of cure. You save a lot of money on drugs if you're just medicating a 10 gallon tank.

Easier to maintain water quality. With newly arrived fish, no doubt stressed by the trip to the fish store and now to your tank, it is imperative to keep the best water quality possible. Many times we buy a group of fish from the store, put them in our main tank, and over the next few days they all die. Taking them back to the store, water tests show that we had poor water quality. Your current fish may be a little used to that water, but the new fish freaked out and eventually died due to it. Doing twice a week 50% water changes in the quarantine tank is fast and easy. Removing 5 gallons and adding 5 gallons of clean fresh water takes about 10 minutes. That's nothing when you think of how it will make your new fish feel!

Better to inspect the fish. If the tank is smaller, the new fish are less likely to hide themselves in the various decorations or plants in your main tank. They only have 5 or 10 gallons to swim in, so they can't stay out of sight for very long. This is important since you need to keep an eye on your new fish to make sure they don't develop any diseases or parasites.

How to Make it Easier

It may sound like a lot of work to setup a separate tank, but since it's a temporary tank and not permanent, the setup only has to last a month or so. Here are some tips to make it easier.

Keep a spare filter on the main tank. This is something a lot of aquarists do for many reasons separate from quarantining. Keep a second (smaller) filter running on your main tank. That way, when you need to setup a quarantine tank you can just move the smaller filter from your main tank to your smaller quarantine tank, and you have an instant cycle! That means the filter will be full of beneficial bacteria to process fish wastes from the quarantined fish.

Use separate buckets and siphon hoses. This will prevent any diseases in the quarantine tank from being transferred to your main tank, thus voiding any benefit you had in quarantining the fish in the first place.

Keep the quarantine tank to a maximum of 10 gallons. If you have a ton of fish purchased, then perhaps splitting it into two 10 gallon tanks would be useful. But in most cases, using a 5 or 10 gallon tank is ideal.

A quarantine tank for new arrivals can also be used as a hospital tank for sick fish.

Use washable decorations and plastic plants. For plants, and hidey holes, you will want to use items which can be bleached or boiled to clean them from all potential contaminants. This includes the standard plastic plants, and ceramic caves and other decorations. Decorations and hiding places are mandatory, as it is not good to keep fish in a bare tank, such conditions will stress them further than they already are.

Use no gravel and make cleaning the tank easier. If you don't bother with gravel then siphoning up fish poop and uneaten food will be a much easier and more thorough job. Chances are your filter can't catch everything. If you have some decent lighting on the tank a bare bottom is not recommended (or at least put some paper under the tank), because having the light bounce off the bottom of the tank can freak out some fish.


The use of a quarantine tank is most often overlooked by the average aquarist. But the experts agree, it is risky at best to introduce new fish into an established tank. At the very least, it could end up being expensive through the use of medication dosing on large amounts of water. If you use a quarantine tank I'm sure you'll enjoy the peace of mind that comes with keeping your other tanks safe from any unknown pathogens.