Lucy

Thanks for the correction SDS.

I don't mean to hi-jack or go off topic, so if this should be a new thread, feel free to seperate it.
If your tank grows X amount of bacteria to accomodate X amount of ammonia produced in your tank, wouldn't losing some of that bacteria also effect the cycle in some way?

My thinking is that since you should only add a few fish at a time so the bacteria can catch up, doesn't it stand to reason if you lose some there may not be enough to handle the ammonia.

Whew, I think I just confused myself. lol

clinton1621

You are correct on both, but usually even if you lose a little bacteria it will rebound in a day or two with no ill effects =)

Lucy

Thanks Clinton

sirdarksol

Think about it this way: Many bacteria need a matter of hours to double their number. In the case of nitrifying bacteria, the number we're looking at is between 7 and 20 (depends on tank temp, amount of available CO2, etc...) Removing half of the filter media probably removes 1/3 (or less, depending on the amount of surface area on the decor) of the nitrifying bacteria in the tank. After this, the colony will "double" within this time period (it will really just stop once it runs out of available ammonia).

The reason the cycle takes so long is that we're starting with a tiny number of bacteria, and those need to double many times over in order to meet the ammonia-consumption needs of the tank. We also need to wait for the second set of bacteria (the nitrite eating ones) to catch up, as well.

(And it may have been a bit of a hijack, but it's info that is good to have if you're doing a filter-switch)