I can't find the site that helped me with this, so I ended up making my own Slow Flow tutorial. This is the cheapest way i have found to slow your filter's current.
NOTE: This tutorial is for small external filters like this one:
On to the tutorial!
You will need:
Very sharp scissors
A water bottle or clean soda bottle.
Cut the top and the bottom of the bottle off, so you have a plastic ring. Trim this ring to be the length of the filter output.
Then, cut the ring so you have a long curvy rectangle:
Bend your curvy rectangle in half, so one side is a bit longer then the other:
Bend again until you have a shelf like part. this part will sit on the rim of your tank.
Next, take your bendy plastic rectangle (boy I am awesome at describing things) and place it UNDER your filter, like so:
and Voila! your own filter flow slower. or whatever you want to call it.