Fishless cycle - high nitrates but not quite done...

[Schlteacher]

I have been fishless cycling my 45 gallon tank. I seemed to be making good progress at first - I got an old filter from a friend and had nitrate reading almost immediately. However, it seems to have stalled now - the nitrates keep getting higher, but I can't get the ammonia and nitrite down to 0. I've been dosing ammonia up to about 2.0 ppm daily and by the next day it's down to 0.25, but never 0. Nitrites also drop, but not enough. I tried doing a 50% water change about a week ago, but that didn't help any - the nitrites actually rose after that.

Am I doing something wrong? Or do I just need to be patient?

 

[Aiken Drum]

It looks like you have been cycling a couple of weeks? My last fishless cycle took 5 or 6 weeks. I found the getting nitrites going to 0 was the longest stage. I wouldnt be worried about doing anything wrong. It looks like you are going in the right direction. It just takes time. 1 month is typical.

Also, try an ammonia test on some bottled water to compare a real 0ppm with your 0.25ppm. If not looked at in good light on a white background a 0ppm reading can look like a 0.25.

 

[Schlteacher]

Yes it's only been a couple of weeks, I just had thought that with the nitrates that high so soon, the nitrites should have been lower by now. I tried the ammonia test with plain water and it did indeed look like a 0.25 to me, so maybe my 0.25 is actually a 0. Thank you!

 

[Aiken Drum]

Each 1ppm ammonia produces 2.7ppm nitrite and 3.6ppm nitrate. So the nitrate will accellerate away when you are dosing 2ppm ammonia. I think the nitrite consuming bacteria (nitrobacter) grows a lot slower than the ammonia consuming bacteria (nitrosomonas) so that stage takes longer. The fact that your nitrites arent getting higher and higher shows you are going in the right direction. I wouldnt be panicking after 2 weeks.

The numbers above assume there is nothing else acting on the cycle, for example plants.