Guppy Acclimation Guide
How to acclimate new guppies without making their first day harder.
The goal of acclimation is to reduce sudden change. New guppies may already be stressed from transport, so focus on temperature, calm handling, stable water, and a gradual transition into quarantine or their new aquarium.
A simple acclimation routine.
The exact process can vary based on how far the water parameters differ, but the main goal is to avoid abrupt temperature and chemistry changes.
Turn the lights down
Dim or switch off strong aquarium lighting before opening the bag. A calmer environment helps reduce visual stress after transport.
Float the closed bag
Let the sealed bag sit in the aquarium or quarantine tank long enough for the water temperature to begin equalizing gradually.
Compare the water
If you expect a meaningful difference in pH, hardness, or other chemistry, transition more gradually rather than moving the fish instantly.
Add small amounts of tank water
When needed, add modest amounts of aquarium water to the bag/container over time so the fish is not hit with one abrupt chemistry change.
Transfer the fish—not the bag water
Use a clean net or carefully pour the fish through a net so transport water does not get added to the aquarium unnecessarily.
Leave the fish alone to settle
Keep lighting calm, avoid chasing the fish around, and give it time to explore before judging its color or activity.
Temperature matching is always important; chemistry determines how gradual the rest should be.
Similar water
If the source and destination water are fairly similar, a gentle temperature match followed by a careful transfer may be enough.
Noticeably different water
When pH, hardness, or other conditions differ more, give the fish a more gradual transition rather than changing everything at once.
Shipped fish
Shipping water can change during transport, so minimize unnecessary time in opened shipping water and focus on a calm, efficient transfer into stable conditions.
Do not automatically pour transport water into the tank.
The water in a store bag or shipping bag may contain waste, medication, pathogens, or chemistry that you do not want in the aquarium.
- Use the bag water only as the temporary transport environment.
- Transfer the fish with a net or controlled pour-through method.
- Discard the remaining bag water instead of adding it to the tank.
- Use clean equipment that has not been shared carelessly between tanks.
What to expect after the fish goes in.
First hour
Color may look dull and the fish may hide, hover, or explore cautiously after transport.
First feeding
Do not panic if appetite is reduced immediately. Offer a small amount rather than trying to force the fish to eat.
First evening
Watch whether breathing settles and swimming becomes more controlled as the fish adjusts.
Next day
Normal appetite, more open fins, and active swimming are reassuring signs that the fish is settling in.
Some arrival stress is normal—but some signs deserve attention.
Can be normal shortly after arrival
- Temporary faded color
- Hiding for a short period
- Reduced appetite during the first feeding
- Cautious or slower swimming while exploring
Check more closely if you see
- Persistent surface gasping
- Severe loss of balance or uncontrolled swimming
- Repeated clamped fins that do not improve
- White spots, visible injury, severe bloating, or rapid deterioration
Do not change everything else on the same day.
Keep the tank stable
Avoid major rescapes, large chemistry changes, or unnecessary deep cleaning immediately after introducing new fish.
Watch social behavior
Make sure the new guppy is not immediately being chased away from food or trapped in one part of the tank.
Check water quality
New stocking increases bioload, so monitor ammonia and nitrite if the tank is young or the stocking increase is significant.
Acclimation mistakes to avoid
- Dumping a cold transport bag directly into a warm aquarium.
- Pouring all store or shipping water into the tank.
- Leaving new fish under intense lighting immediately after transport.
- Chasing the fish around repeatedly with a net.
- Feeding a large meal immediately because the fish “must be hungry.”
- Skipping quarantine just because the fish looks healthy at purchase.