It is now about ime to change my filter cartrage... How can I change it without messing up my levels again?

Why is it time? Is it falling apart? If not then it doesn't need to be changed just rinse it in old tank water. If it is can you keep it in there with the new one for a couple weeks?

what kind of filter, what kind of filter cartriges and how big is the tank. If its a hang on type filter with different levels of media, wash the foam insert in waste aquarium water that you would have in a clean bucket from a water change. Just squeeze it a few times. That should be it for now. Do not wash it in tap water. That will kill the benificial bacteria. The other media can be washed in a week or so the same way. You do not want to do it all at once because you will lose most of that benificial bacteria and most likely have problems with your water chemistry

Depending on what type of filter you have and what other biomedia you have in the tank, that cartridge may or may not be particularly important for maintaining your beneficial bacterial colony. It is mechanical, mostly, with only a tiny bit of biological filtration involved.

Many filters have baskets or places for you to put extra biomedia - sintered glass, lava rocks, ceramic cylindars, bio-wheels. If you have these, you probably do not need that which is in the cartridge. If the cartridge is made of sponge, that may be your main part of the cycle! If the cartridge is just a black frame with some blue floss on it, then it does not hold very much beneficial bacteria, anyway.

As stated above, though, there is really no reason to change out your cartridges the way the cartridge manufacturing companies want you to believe. If the cartridge has carbon chips in it, these can, and do need changing occasionally. If you have been running meds on your tank, the carbon will bind the medications from the water. That carbon now holds the potential to release those chemicals at some time in the future. It is not likely, but it is possible. It is wise to dump that charcoal. To do this, you can slit the blue floss on one end and bang the charcoal out into the garbage. If you wish, you can add exta bio media (from the above list) into the blue cartridge - to add more bio-base to your tank.

I do not count on the filter cartridges to hold my cycle. That is done elsewhere. The cartridges are blasted clean under a stream nozzle I have on my utility tub.

If you wish to preserve anything on that cartridge, though, rinseing them, banging them and rubbing them in a bucket of used fish water will go far to clean them. I use mine until the blue floss is so fuzzy and ragged and falling apart that it stopped filtering as well as it should.

Not trying to be a thread thief, but now that I have an Emperor filter, when I get ready to change the carbon out (Every 2-3 weeks, right?) I plan on rinsing the blue spongy thing and putting a new carbon and floss insert in the filter frame. (I use the three piece cartridges from Drs. Foster and Smith) If the frame is dirty I will rise it as well. Is this too much rinsing? Will it throw off my cycle? How often do you guys take the filter box apart and clean it? I now goldies produce a lot of gunk and it all builds up fast.

I didn't want to make a new thread for a similar question.