The Gorge - Flash Bristow's Website
Beating the Cycle
When setting up an aquarium, it is crucial to establish the nitrogen cycle (as is extensively documented here) and the colonies of bacteria which will break down waste products so that fish are not poisoned.

Usually the cycle process takes several weeks, however when I obtained a second tank I knew my impatience would eat me alive if I had to sit and wait that long! I decided to try seeding the tank with bacteria in various ways, and to try to "beat the cycle". Here are my results, and how you can do it. Note that you don't need an established tank of your own - just a friend or an aquatic shop which will let you have what you need!

I reduced cycling time to just a few days, and was able to transfer my fish across to the new tank straight away. Here I present a description and summary of the method.

My established tank was 2ft long, and the new one 4ft, so I knew I that if I simply took some used filter material from the established tank, it would not be enough to get going right away and possibly not enough even for a kick start, but I had a cunning idea.
A week before I was to set up the new tank, I took a breeding net box, filled it with two types of filter media (floss and ceramic rings) and hung it in the established tank in the flow of the water outlet.

Having set the new tank up a week later, I started the filter with two of the baskets filled with the seeded media from the net in the established tank. I let the filter run overnight because I needed to clear some slight clouding of the water which arose from new gravel etc.

The next day, I added fish. During the day my readings showed no ammonia but nitrite began to rise. It reached 0.3 ppm on day 1.

On day 2 the nitrites rose up to 1.0 ppm, at which point I added a nitrazorb pouch. I also took some gravel and another used filter floss piece, and put them into the tank. (There was nowhere to put the filter floss, so I just stuck it in the tank under a bit of bogwood!) Nitrites came down to 0.3 by the evening. Ammonia went up to 0.025 ppm (i.e. fractionally above 0 but not much) and then back to 0 again.

Day 3, and the nitrites rose again from 0.3 to 1 ppm, so I effected a 30% water change. By evening they had fallen to 0.3 ppm so I removed the nitrazorb and the loose filter floss from the tank.

On day 4 I got up to find the nitrites down to 0.2 ppm. I moved over my remaining fish, and some more gravel from the established tank (as I could now clear it out). Nitrites down to 0.1 ppm and falling despite the addition of a catfish which produces a lot of waste. Ammonia still 0.

On day 5 I bought more fish and the nitrites stayed below 0.1 ppm.

The tank is stable, and the filter coping well, just 5 days after adding water, fish and more fish!

In Summary
  • Seeding filter media initially was very effective in dealing with ammonia from the outset, but not nitrites
  • Seeding again daily from an established tank, even just gravel, seemed to help - perhaps it was introducing nitrite eating bacteria at the right point in the cycle?
  • Nitrites can be temporarily reduced with nitrazorb and water changes if necessary
  • After just a few days the tank seemed to have almost finished cycling, and was stable
I tested ammonia and nitrite every few hours (except overnight when they remained stable in any case) throughout this 5 day period.

There are various reasons why I believe ammonia did not spike but nitrite did:
  • Nitrosomonas (which convert ammonia to nitrite) will remain dormant when there is no ammonia to process. I am not sure whether nitrobacter (which convert nitrite to nitrate) can do this, or whether they die off in the absense of nitrite, e.g. in the first night when I ran the filter
  • Nitrobacter take 15 hours in ideal conditions to double in number, whereas nitrosomonas can do so in half this time. This means an increase in ammonia would be more quickly contained but a nitrite spike is more noticable
  • Nitrobacter growth is inhibited in the presence of ammonia, which means that in a "normal" cycle they will not start to replicate until the ammonia spike has been and gone. Unsure whether this affected my situation
  • Nitrobacter need phosphates present to grow. My tap water is very low in phosphates, so this may have inhibited the speed of reproduction

So in this way the cycle was reduced to fewer than 5 days, with no ammonia spike at all, only a mild nitrite spike which did not affect the fish behaviour or appear to cause any suffering, and I have my new tank stable in under a week!

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This page last updated: 01 September 2022

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