When Should You Perform the First Water Change in a Fish Tank?

The life of a fish keeper in relation to his or her aquarium is dictated by a constant stream of water changes. Whether you keep a saltwater or freshwater tank, you can count on having to do periodic water changes for as long as you have fish species to keep. Even aquarists who only keep plants will have to complete water changes from time to time. The purpose of water changes is to keep the enclosed ecosystem fresh and as healthy as it was a few days after the nitrogen cycle was established and the first few species were introduced.

The First Water Change

When you decide to start a new tank, there will be a few options for establishment and completion of the nitrogen cycle. Seasoned fish keepers will tell you to take your time and start off with the tank, substrate, rocks, decorations, aeration system, and plants. Once you have these elements in place, wait a minimum of three weeks before stocking the tank with hardy fish species. You should wait two weeks before the first partial water change, but only if everything turns out fine.

Quick-Start Tanks

You don’t have to wait weeks to establish a new tank. Many shops offering fish tank supplies sell new aquarium kits complete with bottled bacteria, and these kits allow you to complete the nitrogen cycle usually within a few days. However, you should keep a close eye on the ammonia levels and the overall health of the tank with titration (drip) test kits. A bacterial bloom will unfold over two and three days after introducing the first species, and you shouldn’t change any water during this period unless testing indicates ammonia levels are spiking, which should prompt you to do a 20 percent water change immediately.

The Bacterial Bloom Period

When you stock a new tank with fish, the ecosystem will go through a bacterial bloom period that turns the water very cloudy for a couple of days. This is great news because it lets you know that beneficial Nitrobacter colonies will start settling, and by the time the water clears up on its own you’ll have fully achieved the nitrogen cycle. You should abstain from doing water changes during this period unless ammonia levels are high, which they shouldn’t be. Be patient. A cloudy tank occurs naturally because there’s an explosion of a beneficial living bacterial environment that’s populating by the hundreds of thousands, all in your little new aquarium. It will go away on its own very quickly.

Frequency of Water Changes

After the initial water change, the size of the tank and the bioload will determine how often future changes should be completed. The smaller the habitat, the more frequent these changes should be. In general, if you’re dealing with a 20-gallon tank, a 10 percent water change should be done once a week. Of course, this depends on the results from your test kit, which should be nitrate (<15ppm) and pH (not less than 6.5).

Whether you’re doing your first water change on a new aquarium or you’re maintaining a tank you’ve had for some time, Aquatic Warehouse carries all of the necessary supplies for your aquarist hobby. If you need aquarium monitors or controllers, beneficial bacteria, protein skimmers, testing kits, or any other aquarium supply, stop by our store located in Kearny Mesa or order what you need from our website. If you have any questions, don’t hesitate to call 858-467-9297 to speak with one of our friendly and knowledgeable representatives.