Fish tank owners are divided on this. But most say that there’s no need to let the water sit when you’ve added the water conditioner as the conditioner is already capable of regulating pH levels and alkalinity of the water. If you’re doing a full water change, you can put the fish back 10 to 15 minutes after you treated the water with conditioner. There’s no need to remove the fish if you’re doing a 50 percent or partial water change.
If you’re not using water conditioner, tap water must be allowed to sit for 12 to 24 hours for the chlorine to dissipate. Making sure water conditions are right is important in keeping and maintaining the health of your fish. Otherwise, your fish might find it difficult to adapt to new water conditions which can cause it to feel stressed, or afraid to move around.
Aside from letting the water sit, you also must keep an eye on water temperature. Make sure you have an aquarium thermometer sticking on the outside of your fish tank. You can find one at Waggles Pet Emporium, a pet shop in Bromley selling food and pet care items.