People don't use a lot of purigen do to the cost. The figure major water changes on a frequent basis will do the same job. They are right to a point. Purigen will help with large bio-loads and will also help if the water used to fill the tank has phosphates, nitrates or is discolored. You can't have too much, but you can pack a filter bag to the point that water can't get through the bag and bypasses it instead.