Well actually Fishy...... that is true! However, in an "established" aquarium there
are usually MANY surface areas that "house" the beneficial bacteria....(gravel,
rocks, plants, ornaments, heater and filter tubes, etc.....even some "free-floating"
in the water. So.... that is why it is important to not take any "drastic" steps
when cleaning or doing maintenance on your aquarium. As an example,
for
HOB filters with two sections for cartridges, etc....... it is usually recommended
to change out only ONE at a time!
That said, the only reason to even change your cartridges anyway is:
1- if you want to use some "new" carbon (contained in the cartridge....
because over time the carbon does not properly remove any impurities anymore..
becomes saturated)..
2- the floss (polyester) material becomes "worn" or deteriorated and does not
properly filter out enough debris.
Otherwise you can virtually leave the same cartridges for much longer and
not have any problems. Many folks use sponge or other such filter media
because it lasts even longer and holds even more bacteria!
Hope that gives a little more "insight" there.
On your "nitrites".....keep up the water changing and watch that levels don't get
too high. "Hang in there", it shouldn't be much longer now.
Bernie