So, how do you change a filter without killing off the cycle?
Depends on what kind of filter you are running.
On new setups, just completely avoiding rinsing anything with untreated tap water will benefit your bacteria population.
Since you mentioned changing the filter, I'm assuming you have a Hang on Back filter with multiple cartridges that need to be changed.
If this is the case then simply changing them in intervals is all you need to do.
i.e, change the left cartridge now, change the right cartridge next time, then switch back to left..
This way you will have a constant bacteria population within your filtration system.
Also don't forget that bacteria grows on EVERYTHING.
Your substrate, your decorations, the glass of the tank, any air stone you may have.. So it's pretty difficult to fully 'run out' of beneficial bacteria.
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