Fishless cycling with urea

[Rich]

I am currently trying to cycle my 1st aquaponic system. I have a 400L tank. I added 1 handful of Yates urea 5 days ago, along with 100ml of "cycle" fishtank bacteria and have been testing the water daily. The ammonia levels are 0.75ppm, nitrites 0, pH 7.4. Water temp between 24-28 degrees. I am unsure whether I need to add more urea or does it take time for the ammonia levels to increase using the urea?
I gather that I need ammonia levels to reach 5ppm, then nitrite levels to 5ppm then return to 0. Do I have to keep adding small amount of urea or is there a build up effect. Any advice with regards to using urea to cycle systems would be appreciated

[Hamish]

Have a read of my thread - I added 1 tsp of urea each day until cycled. Perhaps download my diary - links on my thread.

[Jonathan Dyer]

Hamish 1tsp wont do too much the dilution rate is tremendous in 400L and even more in larger volumes. I would start with 300g first week, then another 100g the week after and finally another 100g where I would be adding my plants in the middle of the third week to consume any excess nitrogen . Urea is the inorganic form of urine exact same composition as an organic source, it will take some time to cycle as the bacteria will establish consuming the urea to grow and multiply its there food source, firstly it will be the ammonia bacteria produced in large numbers second will be the nitrite bacteria and finally the nitrate bacteria. This will reflect your tests they should rise quite high on ammonia and drop slightly when nitrite readings pick up and both drop to almost nil when nitrates are at stable levels. At your temperatures it should take three weeks to a month to get fully cycling. Think about putting some aeration into you system now as it will help cycling and reduce the onset of an algae bloom.

[Rich]

Thank you for the info. I will add more urea. I had only added approx 100g. There is plenty of aeration to the system. I'll see how it goes.

[Hamish]

Hamish 1tsp wont do too much the dilution rate is tremendous in 400L and even more in larger volumes. I would start with 300g first week, then another 100g the week after and finally another 100g where I would be adding my plants in the middle of the third week to consume any excess nitrogen . Urea is the inorganic form of urine exact same composition as an organic source, it will take some time to cycle as the bacteria will establish consuming the urea to grow and multiply its there food source, firstly it will be the ammonia bacteria produced in large numbers second will be the nitrite bacteria and finally the nitrate bacteria. This will reflect your tests they should rise quite high on ammonia and drop slightly when nitrite readings pick up and both drop to almost nil when nitrates are at stable levels. At your temperatures it should take three weeks to a month to get fully cycling. Think about putting some aeration into you system now as it will help cycling and reduce the onset of an algae bloom.

My tank is 1250L and 1 tsp per day worked well for me as the graph in my diary shows. I graphed all the water levels and you can see the rise and fall of the Ammonia, Nitrite, Nitrate and pH over the course of a few weeks. I also graphed high and low water temps and air temps.

[Outbackozzie]

JD - you are talking about a huge amount of urea

One hand full does my 8000 litre system fine - gives a small spike.

Remember that urea has lead etc in it as well, so dont go too overboard with it.

[Jonathan Dyer]

The bacteria itself will do it alone but it takes longer, a good dose of urea will boost production of the bacteria no end, test the water to see how it is dropping, adding plants at any time when readings get too high but it can handle high readings prior to fish being added. It is only when the fish are added things needed to be watched. Remember 1kg of salt in 1000L of water increases the reading by 1000ppm or 1ppt same story here.
If things are looking ok then don’t worry it sorts itself out it is a just a matter of preference, but don’t forget the bacteria needs nitrogen to live, too little it takes time, too much and you can cause algae blooms, adding plants solves this a fair amount.

[Rich]

On 10/8/08 I added more urea to my system (200g). At this stage to reading were Ammonia 1, nitrites 0, nitrates 0, pH 7.4. Within 5 days the readings changed to Ammonia 5, nitirites 2, nitrates 10. At this stage I was happy that everything was going to plan. However, over the last 10d the ammonia has continued to increase, the nitrites have dropped and the nitrates have remained stable. Yesterday I changed 1/4 tank water and added more "cycle" bacteria. Current readings: Ammonia 8, Nitrites 0, nitrates 10, pH 6.8.
At this stage I am unsure whether I'm becoming impatient or something has gone awry with adding the urea. Any advice would be much appreciated.

[Outbackozzie]

As I said - too much urea

Way waaaaay too much for 400 litres

An excessively high ammonia reading like 8 actually retards the bacteria, slowing down the cycling process.

Change out 1/2 your water with chlorine free water.

Then be patient - it will cycle

[Hamish]

I hate to say it but if ammonia gets too high I think it can kill off bacteria and undo all your good work - can someone please confirm this? If that is the case then it is evidence that slow and steady adding of the urea wins the race.