I'll check it out. I don't even have dirt in this tank yet.
The purigen is expensive ($18).
What did you top the dirt in the tank with tannins? I have found river sand to be the best. I got it a landscaper co $3 for a 50lb bag. Doesn't need a lot of rinsing and stays clean. Also the color is brown.
Eheim filters are my favorite for they are so quiet. Some don't last long though.