Cycling Question

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QueenKiara

Aquarium Advice Activist
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May 31, 2013
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I know a lot about the initial cycling of a tank, as in using ammonia or dead shrimp or fish food for fishless cycling, or putting a fish in immediately and doing lots of water changes for fish-in cycling. But I was wondering what happens after you've cycled your tank, put fish in, and everything is adjusted, then you add more fish? Lets say you have a tank with four fish in it, then you add two more. Does your tank go through another whole cycle, or does the beneficial bacteria automatically adjust, with no rise in ammonia or nitrites?
 
Hello Shiv...

If you add fish, you start from the beginning and monitor the tank water for traces of ammonia and nitrite. As before, you change 25 percent of the water and replace it with pure, treated tap water. The small water change will remove enough of the dissolved toxins to make the water relatively safe for the fish and provide food for the bacteria to reproduce. You have to grow more bacteria to use the added waste that more fish will produce.

You test the water daily and change a bit if needed. When you have several daily tests that show no ammonia or nitrite, you can add more fish and resume the routine of testing and changing the water. Just do this until the tank is fully stocked.

B
 
Thank you! That's exactly what I wanted to know :) Will it take the same amount of time as the initial stocking or less?
 
The tank should be well adjusted about a week after a new addition. That's how far I usually space out any new additions to my tank and never really have any issues with out of whack parameters.
 
Okay, thank you! This'll be my first time adding new fish after the initial ones, so I wanted to make sure.
 
Fish-In Tank Cycling

Thank you! That's exactly what I wanted to know :) Will it take the same amount of time as the initial stocking or less?

Shiv...

Once the bacteria is established, they reproduce very quickly as long as there is enough dissolved waste in the tank water to feed them. More food, the faster the reproduction process moves. Eventually, you have enough bacteria to use all the ammonia and nitrite for the number of fish in the tank. That's why you have daily tests that show "0" for these forms of nitrogen. The tank is cycled.

Remember, there are no bacteria that uses "nitrates". The nitrates are the end result of the cycle. This form of nitrogen, at low levels, isn't toxic to your fish. Over time, the level will increase and you'll need to perform a water change to remove the nitrates. I change half the tank water at least every 2 weeks. This is enough to keep the water safe for my fish.

B
 
Yes, I do weekly water changes already for the fish I have in my tank, and there are nitrates.
 
Anaerobic bacteria will consume nitrate.

While this is true in order for there to be enough anaerobic bacteria to make any difference in a tank is to run a nitrate filter. I ran one years ago just to see how well they worked and if it truly affected the need for less frequent WC's and well after months of running it, in which you have to dose food such as vodka for the bacteria to use, I found it was a bigger PITA than doing WC's that remove the nitrates and other toxins from water.
 
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