Cycling Without Fish – A Better Method for Your New Tropical Aquarium

Once you have set up your tropical aquarium, the next step is to ‘bike’. This process is the production of beneficial bacteria that will process the ammonia waste from your fish and convert it to nitrite and then nitrate which is relatively harmless. After adding fish to non-recyclable tanks, levels of toxic ammonia and nitrite will rise to dangerous levels until there are enough bacteria to convert them to less toxic nitrates. To overcome this, methods have been designed to promote bacterial growth. The traditional method is to add some ‘hard’ fish which will produce ammonia to encourage bacterial growth while the aquarium is ‘biking’. This method is very stressful for the fish, many of which die or are damaged by the process. The toxic ammonia burns the gills and causes permanent damage.

A better and more humane method of tank cycling is to use the fishless cycling methodIt uses household ammonia as a source, not live fish, and bacterial cultures obtained from healthy tanks or purchased from aquarium suppliers.

Bacterial Starter Culture

You can get a starter bacterial culture by adding some gravel, filter media or rocks from a healthy, old tropical fish tank. If you don’t have the source, there are commercial products available, for example StressZyme or Hagen’s Cycle. Culture will provide a quick start to produce bacterial colonies but you can also use this method without a starter culture. This will take longer than your tank cycle.


Buy 100% unscented and additive-free ammonia. Some aquarium supply stores now sell ammonia for this purpose. If you know a chemist or science teacher, they may be able to provide you with some pure ammonia from a lab supplier.

Tank Temperature

Bacteria (Nitrosomonas and Nitrobacter) thrive best at higher temperatures than those typically used for tropical tanks so during cycling, increase the temperature to between 30 and 35°C (85-95F). When you add fish, you can shrink them again.

Testing Kit

Test kits to check ammonia and nitrite levels are essential to test levels and to indicate when the cycle is complete.

Fishless Cycling Method

Extra aeration is recommended when cycling because bacteria need oxygen to grow. Increase aeration through tanks and filters if possible. You can add extra air stones or even use an extra pump if one is available. Add your bacterial culture, then add about a teaspoon of ammonia for a small aquarium. Upgrade this for a bigger tank. Allow about an hour for the ammonia to circulate, then test. Ammonia levels should be between 5 mg/L (or 5 ppm). Add more ammonia if the level is too low. Leave the tank for a few days then test again.

At this stage the ammonia level should begin to fall and the nitrite level to increase. This means that the bacteria are doing their job of processing ammonia. Add more ammonia when it drops to zero to give the bacteria more to work with. The nitrite level must rise to a maximum and then begin to fall as the nitrite is converted to nitrate which is relatively harmless. Three or four days after the maximum nitrite level is seen, the nitrite level should drop to zero. Cycling is now done.

Change about 50-70% of the water, being careful not to disturb the filter or the gravel layer where the bacteria colonize. Reset the temperature to 25°C, or the recommended temperature for the fish you are referring to and allow the temperature to stabilize for a few hours. Retest for ammonia and nitrite and if the levels are zero you can now start adding some fish.

It is possible after pedaling the tank to add all the fish at once, but this will result in a spike in ammonia and nitrite levels which stresses the fish and can cause them to become sick. Adding fish slowly will allow bacteria to grow to cope with the increased levels of ammonia released by the fish. Even for tanks with full cycles, it is recommended to add fish gradually. Aim to take about a month to fully fill the tank.

The fishless cycle method is more efficient and produces a full cycle tank in much less time than the traditional method of using strong fish. It’s also more humane and you won’t be left with unwanted and often spoiled fish in the end.

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