About once a month, I through away the blue spongy filter pad and replace it with a clean one because I thought that's what it said to do on the filter box. Then I read somewhere that it is bad to throw that away because you're throwing away the good bacteria in your aquarium. The filter also has the permanent bio-filter thing that is beige and stringy looking and I thought that is where the bacteria grow. So should I replace the blue filter pads every month, or is that ruining my aquarium?

I'm mostly concerned because I've had my fish and aquarium set up for 2 months, but recently when I test the water, it has still shown levels of ammonia from .25-.5. I don't know if this means that the tank hasn't cycled, and if so if this is resulting from my changing the filter pad. My fish seem really happy and don't show any physical or behavioral signs of ammonia stress, so I partially wonder if the test strips I'm using are just really crappy. Even after daily water changes, it still shows.