This is a semi rigid pad that you place in a high flow area of your filter. It removes many undesirables, including phosphates and ammonia. Also acts as mechanical filtration. I bought this product for my 2.5 gallon tank at work. I removed the poly floss and cut a piece to fit my nano filter. I got a surprise bonus! As soon as I got it in the filter, it removed all the tannins leached by the driftwood! The water was completely yellowed before I used it, and within minutes was crystal clear. The tank really looks great. I highly recommend this product for a variety of uses. Would make excellent additional layer in your AC filter adding both mech and chem filtration. This product will remove meds from the water.