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     (Fishless Cycling)

A short article on how to mature a biological filter without fish being present and being subjected to “new pond syndrome”. Written by Julian Ward (aka Wardie on koi forums). Thank you Julian for permission to republish it here. Home

Fishless Cycling

This is a summary of how you can successfully mature filter media away from a pond which could be a godsend on a new build to give you a ready to go filter.  Or on an existing pond to boost / add to the filter.  This is just a way I found to do it, I do not claim to have invented the wheel here, just a way of turning it that others will also have worked out.

1. Source a large container, like a plastic dustbin or water butt.  Let us assume it is 100 litres for the purposes of the explanation.

2. Next fill with dechlorinated tap water, remembering not to completely fill to allow for the addition of media. And then add your chosen media at around 50% of the volume - so 50 litres of media.  The photo below shows K1.  Whether you use K1 or not, the vessel will need an air pump to mix the water with the media (as there is no flow through) and to add oxygen. If you don't use K1, simply suspend the media in some netting or onion sacks.

3. For much, much faster results you must seed the media with a mature source.  Otherwise the exercise will take forever. Simply steal some from a friend.

4. Unless you do this in the height of summer, or in the house, you will need a submersible aquarium heater - any old thing will do. I found no gain in heating beyond 20 degrees though.

5. Purchase some household ammonia from “Boots” [“Boots The Chemist”; a large chain of pharmacies in the UK] or such like but beware, the stuff you want is 9.5% strength. There are some weaker ones out there at around 1% which are useless as there is not enough ammonia in there.

6. Start by adding 10 ml of ammonia to your vessel (assuming a vessel of 100 litres, ammonia of 9.5%) will give you a 10 mg/L concentration which is nice and easy to work with.  Obviously there will not actually be 100 litres of water in your 100 litre container - but this doesn't really matter.

7. Use bicarbonate of soda to buffer the water - if you have very soft water add a sprinkling straight away - if not you can add it once things start moving.

8. Test the ammonia level after a day or so to check your progress. It will not take long to start converting if you have added a small amount of mature media.  You can see its progress by also checking for a nitrite read.

9. Once the ammonia has almost gone - add in the same again and you should see that disappear much quicker this time. For example, if it took 4 days to convert your 10 mg of ammonia, expect it now to only take 2 days.

10.  Carry on like this until 10 mg/L has gone overnight and now you can double the amount of ammonia added. CHECK the pH now carefully as you can get caught out. Add bicarb to keep the pH well over 7.0 because if it crashes in the vessel it will knock back your progress by a couple of days as everything comes to a halt.

11.  After several days you will have accumulated a very large nitrite read - do not worry about this at present or even bother to test. Keep increasing the amount of ammonia used so that the following morning you still have a little ammonia left in the vessel. You will be surprised how fast the ammonia bugs get going. Again - watch that pH! (KH)!

12.  After maybe a couple of weeks (if you started with no mature media then expect this to be longer) you should find the media converting quite a lot of ammonia - maybe more than 25 ml (25mg/L) in 24 hours. Again keep a check on the pH (KH even better).

13.  Once the media is happily converting a fair amount of ammonia (maybe around 30 - 40 ml in 24 hours) then you will find it seems to naturally come to a halt.  At this time stop feeding it.

14.  Now you have built up a colony of ammonia bugs on the media which will survive the following steps:

Nitrite stage:

15.  Remove all the media and empty the vessel completely and rinse it out.  Refill it with brand new dechlorinated water and put the media back in. Then repeat this procedure as the media will still be holding a small amount of water which will be sky high in nitrite. Test the water for nitrite to satisfy yourself you have got rid of most of it.

16.  Simply feed the original small amount of ammonia (10 ml) to the new water to give you a controlled nitrite read.  Now you will repeat the whole maturing process but this time you will not test for ammonia - but nitrite instead. Once the nitrite has dropped, simply add more ammonia in exactly the same way as before. WATCH that pH! (KH)!

17.  You should be able to get the nitrite converting to a similar rate at which you got your ammonia reducing in the first stage.  How long this takes depends on how good a 'seeding' you provided in the very first place. Do not worry about the ammonia bugs not getting enough to eat - this doesn't appear to matter. Even if they die back a bit, the speed they come back in the vessel makes this nothing to worry about. Try not to let the nitrite run out, but don't overload it.

Once it is consuming both the ammonia and now nitrite overnight in decent quantities - it is all ready to go into your pond filter.  Once it is in, make sure you feed the koi plenty to keep all your hard work alive.

Remember to watch that pH and or KH, as I guarantee it will catch you out at least once, it did me.  Occasionally I found the water got totally messed up - i.e. the pH would, for some reason, rocket to way over 9, when this happened it seemed to halt the proceedings. The best way I found around this was to swap the water out again.

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