How long should I float the bag?

The CDC says to float the sealed bag for about 30 minutes to an hour; Aqueon's kit guide says 20 minutes before mixing in tank water; an older Purdue 4-H manual says at least 15 minutes.

Should I pour the bag water into my tank?

Try not to. The CDC says not to pour too much water from the bag into your aquarium because of the germs it may contain.

Should I quarantine new fish?

UF recommends quarantine for all new fish before adding them to an established system, which may last 1 to 8 weeks, and the CDC suggests a second tank for new fish.

How to Acclimate New Fish (and Why to Quarantine Them)

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Quick answerFloat the sealed bag in your tank to match temperature (the CDC says about 30 minutes to an hour), then gradually mix in small amounts of tank water so the fish adjusts to your water chemistry. Net the fish into the tank and discard the bag water rather than pouring it in. If you can, quarantine new fish in a separate tank first.

Moving fish from store water to yours is a shock to their system. The University of Florida describes acclimation as "slowly introducing the fish to different quality water to allow physiological adjustments to occur gradually." Here's how.

Step by step

Float the bag. Float the sealed bag at the surface. CDC: "for about 30 minutes to an hour." Aqueon's kit guide uses 20 minutes.
Mix in tank water gradually. Aqueon: "Open bag and add about 1/2 cup of aquarium water. Wait 5 minutes. Repeat once." UF says acclimation means "gradually adding water from the holding tank into the transport container."
Move the fish, not the water. CDC: "Try not to pour too much water from the bag into your aquarium at home because of the possible germs it may contain." A soft net helps.
Go slow if temperatures are very different. UF: if the difference is greater than 10°C, "acclimation should proceed slowly over a period of two or more hours."

Fine-mesh net

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3 x 2.5 in. fine nylon net, per the listing
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Thermometer

AQUANEAT Digital Aquarium Thermometer

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Quarantine

UF: "Quarantine is recommended for all new fish prior to introduction into an established population," and isolation "may last from 1 to 8 weeks." Another UF fact sheet says the same for plants. The CDC suggests "a second aquarium ... to house new fish before you place them in your established tank." A small tank with a sponge filter and heater works.

Sponge filters

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50W heater

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After they're in

CDC: if a fish looks sick, "remove it and place it in a tank by itself."
Purdue Extension's 4-H manual: "Wash hands before and after caring for fish."

FAQ

How long to float?

About 30-60 minutes per the CDC; 20 per Aqueon.

Pour bag water in?

No.

Quarantine?

Yes, 1-8 weeks per UF.

How to Acclimate New Fish, Step by Step