RE: Purigen
My suggestion is that if you are having nitrogen problems then you probably need to adress the issue with why before looking for a silver bullet type of cure.
Amoonia and nitrite are processed by bacteria in a wet/dry, live rock, and the surface of your substrate. Its also removed by skimming and carbon filtration. Generally, in most systems, the presence of nitrite and ammonia is an indication that you are either over stocking live stock, or over feeding, or that you have had some sort of die off.
Nitrates are processed by bacteria in low oxygen areas of the tank. Generally, this is in deep sand beds and deep pores of live rock. The presence of excess nitrates is common in tanks without an adequate deep sand bed, or that are overstocked or overfed. Again, skimming and carbon filtration can help out here.
A refugium is also very helpful in lowering nitrogen wastes. It's fertilizer to the plants there.
Gary
125 SPS, 75 gal. LPS/softie reef, 9 gal. Nano