Cycling the Tank

By John H. Tullock
Copywright ©1996 All rights reserved

"Cycling" your marine aquarium basically means growing beneficial bacteria in the filter before you add any fish. When the tank is cycled, the filter can remove fish wastes. If the tank is not cycled, the fish will be forced to swim in their own waste products. This, in turn, will cause them to become sick, and perhaps to die. So cycling properly is very important. The method described below takes about a month.

You will need to test the water several times during the cycling process. You can bring a sample in to your dealer for testing. It is much more convenient, however, if you have your own test kits. The basic ones are not expensive, and are easy to use.

Step-By-Step Method

1. Add enough 6% ammonium chloride solution (approximately 1/2 teaspoon per 20 gallons will be needed) to give an ammonia test reading of 1.5 - 5.0 ppm.
2. Wait 24 hours. Test ammonia again. If lower than 1.5 ppm, add another 1/2 teaspoon of ammonium chloride solution per 20 gallons and test again.
3. Repeat as needed until the ammonia reading remains stable between 1.5 and 5.0 ppm overnight.
4. Add one pound of cured live rock or rubble per 20 gallons.
5. Wait 5 days, and test for nitrite. Make a note of the date and the test result. Repeat the nitrite test every 2-3 days. Be sure to write down the date and the test result each time.
6. You will see from your nitrite test results that the level of nitrite in the tank starts off slowly and then increases until the liquid in the test vial becomes very red. It remains like this for a while, and then drops off, finally reaching zero. When the nitrite level reaches zero, this indicates that you have grown a very large population of beneficial bacteria.

Before You Add Fish to Your Tank

1. Test the water for nitrate. (Notice that nitrate and nitrite are two different things.) If the result is greater that 12.5 mg/l, you should change about 1/3 to 1/2 the water in the tank before you add any fish.
2. Also test the pH of the tank at this time. If the pH is lower than 8.0, change 1/3 to 1/2 of the water in the tank before adding animals.

You can add new animals every 10 - 14 days. Remember not to overcrowd your tank. Do not try to put large fishes into a tank that is too small for them. Check with your AMDA for advice on stocking your tank.

It is wise to check ammonia and nitrite levels before, and a few days after, adding new animals. If either of these tests is anything other than zero, do a partial water change immediately. A positive test for either ammonia or nitrite indicates that your filter bacteria are not doing their job properly. In this situation, it is important to take quick action to protect the health of your fish and/or invertebrates.  About a week after you add your first fish, and each week thereafter, you should test both pH and nitrate. Write down the date of these tests, and the test results.

Schedule a water change of 20 - 25% when nitrate rises above 25 mg/l or when the pH falls below 8.0. If nitrate seems to rise very high in a short period of time, you may have too many fish in the tank, or you may be feeding them too much. Consult with your AMDA dealer for advice.