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For this method, we'll start with a fully-assembled tank, minus the fish, just like in the method above. However, this time, we won't add the fish until the entire cycle is completed. Instead, we'll add biological waste manually as we monitor the water level and wait for the cycle to complete. This method requires a lot of patience, as it requires you to wait for the organic material you add to your tank to decay and start producing toxic waste products. However, it's often considered a more "humane" option as it doesn't expose fish to ammonia and nitrites like the method above does. To begin, drop just a few flakes of fish food into your tank about as much as you'd use to feed your fish will do. Now, simply wait. Over the next few days, the flakes will begin to decay and release waste products (including ammonia) into the water. Use a test kit (or bring a water sample to your local pet store) to test your water for ammonia levels. You want to have a level of at least three parts per million (ppm). If you don't have enough ammonia in your water, add more flakes and wait for them to decay before testing again. Continue to test your water every other day for ammonia levels. As beneficial bacteria begins to grow in your aquarium, it will start to consume the ammonia, reducing the ammonia levels. Replenish them by adding fish flakes whenever the ammonia level falls below three ppm. As the bacteria start consuming ammonia, they'll begin to produce nitrites, the intermediate type of chemical in the nitrate cycle (which is less toxic than ammonia but still harmful to fish). Start testing for nitrites after a week or so again, you can use a commercial test kit or take water samples to a pet shop to do this. Once you detect nitrites, you'll know the cycle has started. At this point, you'll continue adding ammonia as you have before. As you feed the bacteria in the tank ammonia, the nitrite levels will continue to rise. Eventually, however, enough beneficial bacteria will grow to convert the nitrites into nitrates, the final type of chemical in the nitrate cycle (and one that isn't harmful to fish.) When this happens, you'll know the cycle is nearing completion. You can detect this final phase of the cycle by either testing for nitrites (in which case you're looking for a sudden drop), nitrates (in which case you're looking for a sudden spike from a base level of zero), or both. After about six to eight weeks, the ammonia and nitrite levels should decrease to a level that's so low you can no longer detect them, while nitrate levels should plateau. At this point, it's safe to add your fish. However, as in the method above, you'll want to add your fish gradually. Don't add more than a few small fish at a time and wait at least a week or two before introducing your next batch of fish. Consider cleaning the substrate with a siphon hose before adding fish, particularly if you had to add a lot of food. Decaying food or plant matter can become a ticking time bomb. If it gets trapped in the gravel, the ammonia won't enter the water, but if something upsets it, it could release a fair amount of ammonia rather quickly.
Assemble and prepare your tank. Add a sprinkling of fish flakes. Test your water for ammonia in a few days. Try to keep the ammonia level at about three ppm. Start testing for nitrites, after a week. Wait for a sudden drop in nitrites and a rise in nitrates. Add fish gradually when ammonia and nitrite levels are near zero.