If you google Seaklear phosphate remover. You'll find lots of places that sell this stuff in the US and ship. I'm from Canada and had to buy from the US. Seaklear was nowhere to be found in Canada.
Here's a place that sells the Seaklear Aquaria(it's the same thing as the seaklear for pools) and they sell filter socks too.
http://www.aquaticeco.com/