Cycling Tank - The Restart

6mls is a bit of an overkill, you’d get a quicker cycle with 1 or 2, and you’d still have enough bacteria...
Watch the nitrites don't exceed 15mls or they’ll stall the cycle... high nitrates will slow it down also...

Can you link me to it?

I think it’s my fault... you’ve added 6mls in total, not 6mls per litre...?

So you’ve got 6mls in 200l, which is 0.03mls/litre. That’s not much. You’d be better off with 1-2mls/litre.

D’oh.

That’s fine. Just ignore me, it’s one of those days...

The main reason that 3 ppm was chosen in the method that I used in that link is that it is more than a sensibly stocked tank will make per day, so you know that you have grown more than enough bacteria by the end. Of course it won't be enough for a grossly overstocked tank.......

At the very start of the cycle, you add enough ammonia to get 3 ppm in the water. This is dose 1.

You reach stage #6 when the first dose of ammonia drops to 0.75 ppm and it has been turned into at least 2 ppm nitrite.
When you've reached this target add 3 ppm ammonia. This is dose 2

The next bit is difficult to explain properly.
Once you've added dose 2 you start testing every 2 days instead of every 3 days.
Then you wait until ammonia has dropped to zero, and when you test 2 days later it is still zero. You must have two zeros, two days apart before going on to the next stage.

Once you got these two zeros, add enough ammonia to get 1 ppm in the water (stage #8). This is dose 3.


Now it's just a question of testing every 2 days and waiting till you get the target levels in stage #10.
Until you get to those targets, you add a small (1 ppm) dose of ammonia when ammonia readings show zero at two tests two days apart. This is to feed the ammonia eaters while waiting for the nitrite eaters to grow. Depending just how fast ammonia drops to zero, this could mean adding 1 ppm ammonia 4 days after adding the last 1 ppm dose if the readings drop quickly or longer than 4 days if the reading drops slowly.



I've added the dose numbers to the sticky.

With mature media it is possible that you have enough nitrite eaters to remove nitrite as soon as it is made by the ammonia eaters. In this case you wouldn't see a reading for nitrite as it would all have been converted to nitrate as soon as it appeared.

I would wait till ammonia drops to zero and if nitrite still hasn't shown up, add another 3 ppm.


The target points and timescales in the method assume that no mature media or bottled bacteria are used; they can alter the progress of the cycle so when they are used the cycle will be different.

Hi all

Just a little update on both tanks.

The 200l has been going for 6 days, and now reading 1.62ppm for ammonia and no nitrites yet. There are no plants in this tank.

The 125l has been going for 5 days, registered 0ppm ammonia yesterday, so I added 3ppm yesterday, and todays reading is 1.05ppm. Still zero nitrites. There is some mature media in this tank and half a dozen plants.

So the 125l tank is showing 0.60ppm ammonia and the slightest hint of nitrites. The lack of nitrites could be because of the mature media already having the nitrite bacteria.

I think I will check again tomorrow, and if ammonia is nil, do another 3ppm ammonia dose and check every two days. Does that sound like a plan?

I would do just that. When ammonia drops again, test the tank nitrate and the tap nitrate to see if they are the same or not. If tank nitrate is higher, it must have come from somewhere - from all the ammonia you've added.

So ammonia down to zero. Nitrites zero. Nitrates out of tap 10ppm, out of tank 40ppm, so definitely seems nitrate being produced.

Have added 3ppm ammonia and will check in 2 days to see if zero. If it is, will check in 2 days again and if still 0ppm, do I add 1ppm ammonia at that point?

Without mature media or Tetra Safe Start it can take a while to drop. I had the same thing happen - ammonia dropped but no nitrite then stayed at the same level for a while. It took 21 days for my ammonia to drop to zero with no mature media or TSS, though every tank is different.