Hi guys Im new as an aquarist or better yet im new at oscar fish. Im currently doing fishless cycling now with my 75g tank. I been putting ammonia about 7ml to peak to 5ppm. My nitrite spike in couple day, so I cut down my ammonia to about 3-4 ml a day. after almost 3 weeks, my nitrite reads 0 and my ammo reads 0 and my nitrates reads about 180 (API test Kit) for the past 2 days. I though my tank is cycled, so I did about 75% water change. I also put airstones in my tank before i feel it up with water again. Heres the problem, My nitrite reads again about 5 ppm, ammonia reads 0, nitrate read 40ppm. How could that be? My tap water reads 0 nitrite, nitrate and ammonia is also 0. I current have 400 emperor filter and magnum 350 filter on it. I only take the carbon out in my magnum 350 and add bio balls on since "charcoal can cause hith so as rumors but not proven". I also add API stress coat to remove chlorines and chloromines while putting a new water for my oscar. Please explain why my tank is still not cycle after stating for 2 days that nitrite is 0.

I assume you've got no fish are now at the moment? When you did the 75% water change, did you use a water Dechlorinator?

Yea, I don't have any fish there, they are in my 12g for now. And yes I use API dechlorinator. Until now my nitrite seem to be at 5... my ammonia is 0. IS it going to begin cycling again? I realy don't know what I did wrong or could have done to prevent this.

When you do fishless cycle, you are not supposed to use any kind of Dechlorinator when doing a water change. If you do, this can apparently cause the problem you've had with the nitrites. Why? I have no idea. This might not be why this happened, it's just something to bear in mind, next time, don't use a Dechlorinator and see what happens. Obviously when you finally put fish in, you will have to use it.

I would continue to put a very small amount of ammonia in until your nitrite and ammonia stay at zero. You may find that your nitrite is very high, it may take more than one water change to bring that down to an acceptable level.

if u can borrow sum gravel,media,ornaments or anything u can get hold of from a cycled tank that will speed up the cycle and put a few guppies in there