i want to upgrade my filter to penguin bio-wheel - either 200 or 350 for my tank (it is a 20 gallon long and will upgrade to a bigger tank later on) which has guppies, apple snails, ramhorn snails, and live plants. i might add eco-complete gravel to my tank soon.. so, i need to figure out what can i make the penguin bio-wheel work without carbon because i don't like actived carbon. is there anything else i can use instead of carbon? i'm currently using a tetra whisper 20 and i hate it with a passion. so, i need to figure out quick before it ruin my tank.