If you're anything like me, the most frequent and annoying cost is replacing your filters. Sure, you can get away with rinsing them a time, maybe two if you do it often, but what is the overall worth of continuing to buy every week or two? While there are plenty of benefits to buying prefab carbon filters in little packages with frames, there are cheaper options that can also be very beneficial for your fish, your wallet, and your knowledge about the way a tank cycles. If you have a smaller tank with a standard hang on the back canister filter, not much can be done in the way of adding biological media (I'll go over bio and mechanical media in a later blog) but it won't make too much of a difference as long as you are doing regular water changes and making sure the water is healthy. My best friend in the world when it comes to filtration is polyester sheeting. You can buy it anywhere for only a couple dollars a roll, and a roll will last for quite a while. Think of it as spending what you would on one filter (so a week or maybe two of use) on a whole roll of polyester that will last you a month or more. Just cut a strip about as wide as your filter tank, double it up, and put it into the filter where the replacement would go. Change it out every couple of days and you are good to go. Using only polyester is a perfect way to cut costs in tanks 20 gallons and under that aren't pushed to their capacity. Keep in mind that the amount of fish you keep will dramatically change the quality of your water and their health. I will talk about ways to cheaply filter your bigger aquariums soon. Until then, enjoy.