umm I dont think you are suposta change the bio part of your filter...ever, and I would just swish it around in some old tank water if it gets filthy...any other way and you are removing a huge part of your benifical bacteria either by throwing them out, or rinsing them in tap water...the water straight out of the tap has the nasty stuff that kills the bacteria.
this could be why...if you are throwing out the part of your filter that contains the bacteria, you could be nearly starting a fresh cycle every time you change filters.
I over filter the heck out of my 29 gallon...I have a 10-20 gallon filter and a 20-40 gallon filter, it gives the good bacteria more room to spread out. and my fish like to play in the water current.
I wouldnt use the carbon filter unlese you have to, the carbon removes ammonia, but eventualy stops doing that and leaches it back into the tank, I would just get more sponges and ceramic rings to fill the space.
if I am retelling you things you already know or soembody else told you, sorry, just trying to help. hope things calm down in your tank soon