Andy M Fishless Cycle

That's where I have the advantage - we aren't on a meter!

Your cycle looks like it's behaving nicely and it won't be long before it's finished.

Day 24

Ammonia zero

Nitrite zero,  dosed 4ml ammonia to 4ppm ( yet to retest)

Should I check in the morning now although it won't quite be 12 hours before I go to work ?

Thank you Sue, will do that

Day 26

12 hour test

Ammonia 0.5 ppm

Nitrite around 5 again

I found the ammonia was zero at the 12 hour test once I started testing then, probably because it had all the time while the nitrite level was still high to grow enough ammonia eaters to remove all the ammonia quickly. But it took a few days for the nitrite to drop to zero at 12 hours, and I only went up from 1 to 2ppm ammonia (25 litres with 1 betta is understocked so I didn't need any more)

Just checking my records, I find that my nitrite never did get quite to zero at 12 hours. I got a betta when it reached 0.25. I did keep an eye on both readings for several days after I got the betta and never saw a trace of either of them.

It may not drop all the way to zero, mine didn't. But as long as the 24 hour nitrite is dropping to zero and the 12 hour is getting low you should be OK for fish. Just monitor both ammonia and zero twice a day as you are at the moment and you'll soon spot if there is either of them showing up. I've recently come across references to 3ppm being all you need. If 3ppm is all you need and your 4ppm isn't quite dropping to zero nitrite in 12 hours, you should be fine.
Don't forget to do a big water change shortly before you get the fish, especially if there is still a trace of nitrite in the water after 12 hours. Ideally, do the water change then go out shopping. Have you tested your nitrate? You'll probably find it's quite high now that you have nitrite eaters - that is why you do the big water change, to get rid of the nitrate.

Yes, nitrite does really need to be lower than 5ppm. Is it still reaching zero in 24 hours? If it is, I'd say wait till the 12 hour reading gets below 1.
Under optimum conditions (though our tanks are rarely spot-on optimum) these bacteria can double in 24 hours. It is just a waiting game now.

Day 26

24 hour test
Ammonia zero
Nitrite zero so dosed to 4ppm again
Nitrate I can only describe as a deep red colour, certainly not like anything on the chart

So as and when the nitrate is down, how does it stay down?  Purely water changes?

Removing nitrate, and replenishing things that get used up, is the main purpose of water changes. There are all sorts of other things we can't measure (eg fish hormones) that also build up and water changes remove them too. The nitrate level is something we can measure and it can be used as an indicator for all the other things as well.


With a tap level that high, 40ppm is the lowest you'll be able to get your tank nitrate by water changes alone. This is not a problem for the vast majority of fish. They can tolerate levels up to 100 with no problems. But there are some nitrate sensitive species. Reasearching before buying should flag up if any fish you want would suffer. Planting the tank heavily (and I mean more than just a dozen plants) can help lower nitrate but to get really low you would need to use something like RO water (water that has had everything dissolved in it removed). This is not a step to take lightly, and I would only recommend it once you get further into fish keeping and want to keep some of those nitrate sensitive fish.
The UK allows up to 50ppm in drinking water.