Basis of Tank Cycling

[mitchrapp]

Just curious as to the basis for knowing a tank is cycled when ammonia and nitrites drop to 0 within 24 hours. Ammonia i can kind of understand due to its toxicity, but why 24 hours and not any other increment? According to Randy Holmes-Farley's article (http://reefkeeping.com/issues/2005-06/rhf/index.php), nitrites aren't toxic to marine fish at levels likely to be encountered in our tanks (LC50s in the 100-300 ppm range). So why is waiting until nitrites dropping to 0 within 24 hours an indicator of when cycling is done?

Also what is the basis for the concentration of ammonia dosing? I commonly see 2 ppm referenced, but does this correspond to a typical bioload?

[jminick2]

Just curious as to the basis for knowing a tank is cycled when ammonia and nitrites drop to 0 within 24 hours. Ammonia i can kind of understand due to its toxicity, but why 24 hours and not any other increment? According to Randy Holmes-Farley's article (http://reefkeeping.com/issues/2005-06/rhf/index.php), nitrites aren't toxic to marine fish at levels likely to be encountered in our tanks (LC50s in the 100-300 ppm range). So why is waiting until nitrites dropping to 0 within 24 hours an indicator of when cycling is done?

Also what is the basis for the concentration of ammonia dosing? I commonly see 2 ppm referenced, but does this correspond to a typical bioload?

No one knows what a typical bioload produces in ammonia because when that time comes its being converted so fast you cant get a reading. One way to find out would be to buy everything you want pre cycle and throw it in your tank all at once and see what the ammonia spikes to....but we all know that's not a good idea. It also doesn't matter if 2ppm would be enough once the bacteria become efficient at converting ammonia they multiply so fast to "handle" the bioload that's why people say add it slowly so it can catch up accordingly.

Also you want to let the nitrite drop accordingly with in that time frame because just like the microbes that convert ammonia efficiently the microbes that convert the nitrites also need to become efficient before adding the livestock otherwise it could build up. Whether or not it could build up to toxic levels I do not know. You also cannot convert ammonia to nitrates only nitrites to nitrates and corals need a little bit of nitrates IMO to thrive

[jminick2]

Azendake a guy on this forum will tell you that feeding what you plan to feed your bioload daily during a cycle will set your bacteria population to around the amount of ammonia is being produced. The idea is sound, I think there a lot of variables though that will make this close to being right but not dead on. I also don't think its needed. The bacteria will always adjust on their own with or with out doing this.

[homer1475]

Azendake a guy on this forum will tell you that feeding what you plan to feed your bioload daily during a cycle will set your bacteria population to around the amount of ammonia is being produced. The idea is sound, I think there a lot of variables though that will make this close to being right but not dead on. I also don't think its needed. The bacteria will always adjust on their with or with out doing this.

I can totally understand this theory, and its a sound practice to ghost feed for cycling, but how on gods green earth will you ever know what your eventual bioload will be?

Most people have a stocking idea, but end up with more then they originally planned, cause you know we all impulse buy from time to time.

[gone fishin]

Jminick gave a pretty good reply. I would speculate the 2ppm number came about through peoples experiences, like so many other things in this hobby.