Cycling a Tank

Although new fish hobbyists purchasing their first fish tanks want nothing more than to stock that system with colorful cichlids or graceful angelfish, pet store owners should curb their customers’ enthusiasm--just for a little while--and teach them how to cycle their tank before adding the fish.

Cycling a tank essentially involves building a population of beneficial bacteria in the filter media and substrate that removes toxins produced by fish from the water. Fish living in tanks that aren’t cycled properly fall victim to the dreaded new-tank syndrome and often meet their early demise. And for retailers, that could mean the loss of a new customer.

Before retailers start explaining how to cycle a tank, however, they should be sure the customer understands the nitrogen cycle. When fish urinate or defecate, they produce ammonia, which is deadly in high doses. In a properly cycled aquarium, nitrifying bacteria consume the ammonia and turn it into nitrite, which is then oxidized by other beneficial bacteria into harmless nitrate. If those bacteria aren’t present in the system, the fish would literally die in their own waste.

Here are some basic tips for cycling a fish tank to share with new aquarium owners:

1. Remove chlorine and chloramines: First, fill the tank with tap water and add a water conditioner, following the instructions on the label. Chlorine and chloramines, which are present in tap water, don’t mix well with bacteria. Removing them is the first step in creating an environment suited to living things.
   .
2. Put fish in the water: Next, customers will want to add some hardy fish to the water. Guppies, tetras and barbs make good (and relatively inexpensive) choices to start with. Place them in the tank and feed them the amount recommended by the manufacturer--and no more. Too much leftover food will create toxins, too.
   .
3. Test the water: The next day, customers will need to test the water for ammonia, nitrites and nitrates to determine how the tank is progressing. Throughout the process, they’ll need to check the levels and do water changes when necessary. Do a 25 percent water changes every other day, depending on how the ammonia levels look.
   .
4. Welcome Nitrospira: In a couple of weeks, the beneficial bacteria will begin to develop and consume the ammonia in the tank, turning it into nitrite. At this point, customers will see the ammonia levels decrease and the nitrite levels increase. Eventually, another beneficial bacteria will develop to consume the nitrites, turning them into harmless nitrates.
   .
5. Add fish--but do so slowly: Once the tank is cycled, customers can begin adding their favorite fish. Encourage them to do so cautiously, however, to give the tank time to build sustainable populations of beneficial bacteria.