New fish are exciting, and they're also one of the most common ways diseases get into a healthy aquarium. A quarantine tank fixes that. It's a small, separate setup where new arrivals wait out a few weeks before joining your main tank. The same tank doubles as a hospital tank when a fish gets sick. Here's exactly how to set one up, how long to use it, and what to buy.
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Because you can't see what a new fish is carrying. Dr. Jessie Sanders of Aquatic Veterinary Services, board certified in fish practice, says all new fish need 4 to 6 weeks in their own separate system, no matter what the seller promises about being disease free. Quarantine gives hidden illness time to show up where it can't spread.
It also protects the new fish. Shipping and a new home are stressful, and University of Florida extension specialists (FA084, 2025) note that stress weakens fish immune systems and opens the door to bacterial infections. A quiet, stable tank is the best place to recover from the trip.
Set it up before the fish arrive. You need a separate tank with a heater, a filter, conditioned water, and its own net, because a shared net or bucket can carry disease right back to your main tank. A bare bottom makes it easy to spot waste and clean, and a hiding spot or two helps nervous fish settle.
| Item | Why you need it | Our pick |
|---|---|---|
| Tank | A separate system so problems stay contained | 20 or 29 gallon starter kit |
| Heater and thermometer | Stable temperature lowers stress, and you'll need to match temps later | Mini flat heater + digital thermometer |
| Filter | New fish make waste from day one | Adjustable 10 to 50 gallon filter |
| Water conditioner | Makes tap water safe for fills and water changes | 16 oz conditioner |
| Dedicated net | A shared net carries disease between tanks | 2.5 inch net or 5-pack |
| Medication on standby | Shipping takes days when a fish gets sick | Fish Dox, Fish Sulfa, Fish Zole |
Keep quarantine gear separate from your main tank, and never share nets or buckets.
20 Gallon Aquarium Starter Kit with LED Lighting
An all-in-one kit that makes an easy, roomy quarantine tank.
$196.29 Shop Now →
Glass 29 Gallon Aquarium Starter Kit
Extra water volume for quarantining larger fish or groups.
$151.24 Shop Now →
Mini Flat Heater for Small Aquariums
Keeps a small quarantine tank at a steady temperature.
$13.18 Shop Now →
Adjustable Fish Tank Filter, 10 to 50 Gallons
Adjustable flow for stressed new arrivals.
$26.28 Shop Now →
16 oz Aquarium Water Conditioner
Treat the tap water you use to fill and top off the tank.
$23.68 Shop Now →
Stress Zyme Bacteria Supplement
Helps a new quarantine filter build up beneficial bacteria.
$16.68 Shop Now →
Purigen & Matrix Bio Media, 250 ml
Bio media and waste control for a small filter.
$19.84 Shop Now →
Acclimate slowly, watch closely, wait 4 to 6 weeks, then match the water before moving. Aquatic Veterinary Services recommends floating the open bag and adding a small amount of tank water every 5 minutes until the volume doubles, then gently netting the fish into the tank. The first 10 to 20 minutes are critical, so don't walk away.
During quarantine, watch appetite, breathing, fins, and behavior every day. When the time is up, check that the quarantine tank's pH is within 0.5 and its temperature is within 5 degrees Fahrenheit of the main tank before you move the fish, as Dr. Sanders advises.
Yes, and it should. University of Florida specialists warn that antibiotics added to the water can kill the nitrifying bacteria in a biological filter, so treating in a separate tank protects your main system. Keep a broad-spectrum medication on hand so you can act fast if something shows up during quarantine.
Not sure which medicine fits which problem? Our Fish Mox vs. Fish Dox vs. Fish Zole vs. Fish Cipro guide explains each one, and our fin rot guide covers the most common problem in new fish. For water testing basics, see Aquarium & Fish Health 101. Medications are for ornamental fish only; always follow the label.
Fish Dox 100mg Capsules, 30 Count
Broad-spectrum doxycycline to keep on standby during quarantine.
$43.99 Shop Now →
Fish Sulfa 960mg Tablets, 30 Count
A broad-spectrum option for fin rot and ulcers.
$32.95 Shop Now →
Fish Zole 250mg Tablets, 30 Count
Metronidazole for internal parasites such as Hexamita.
$33.99 Shop Now →
Once your new fish graduate from quarantine, give them a main tank worth the wait. Here are picks from a compact stand to full showpiece aquariums.
Metal Aquarium Stand for 20 Gallon Long
A compact stand with shelf space for your quarantine supplies.
$99.27 Shop Now →
LED Planted Tank Light, 4 Channels
A remote-controlled light for your main display tank.
$64.63 Shop Now →
Power Aquarium Filter, 3-Step, 30 to 60 Gallons
Strong filtration for the main tank your fish will graduate to.
$78.99 Shop Now →
140 Gallon Seamless Glass Bowfront Aquarium with Cabinet and Canopy
A real-wood showpiece for a big, healthy community.
$4,450.00 Shop Now →
170 Gallon Panoramic Reef-Ready Aquarium Set, White
A panoramic glass centerpiece with matching white furniture.
$6,499.99 Shop Now →
Board-certified fish veterinarian Dr. Jessie Sanders of Aquatic Veterinary Services recommends 4 to 6 weeks in a separate system for every new fish, even if the seller says it's disease free. That window gives hidden problems time to show up before they reach your main tank.
Big enough to keep water stable for the fish you're adding. A 10 or 20 gallon tank works for most small community fish. Larger fish or groups need more room. More water volume means slower swings in temperature and waste, which keeps new fish calmer.
Yes. New fish produce waste from day one, so the tank needs filtration and a heater. A simple sponge or hang-on filter is enough. If you treat in the tank, remember that some medications can harm the filter's beneficial bacteria, so test the water more often.
Match the water first. Aquatic Veterinary Services says it's safe to move fish when pH is within 0.5 and temperature is within 5 degrees Fahrenheit of the main tank. Net the fish gently, add it, and watch closely for the next few days.
Yes, and that's one of the best reasons to own one. The same setup lets you isolate a sick fish and treat it without exposing your main tank's filter, plants, and other fish to medication. Keep it clean and ready between uses.
Sources: Dr. Jessie Sanders, DVM, DABVP (Fish Practice), Aquatic Veterinary Services, How to Safely Add New Fish, retrieved 2026-10-05. University of Florida IFAS Extension, Use of Antibiotics in Ornamental Fish Aquaculture (FA084), updated 2025, retrieved 2026-10-05. This article is general information, not veterinary advice.
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