Purigen is a pretty good water clarifier but because it filters so well it when it gets exhausted it can slow flow. I was using one bag in my Rena and upon exhaustion it had slowed the return flow to a crawl. As long as you do regular filter maintenance and follow purigen's regeneration process you should be good to go. Though if ou could post up pics of the tank with the yellowish tinge we maybe able to suggest a better alternative. I only say that since you say it turns yellowish in about a week you might be suffering from free floating algae blooms and in that case a UV Clarifier would be a better alternative and depending on tank size and other factors might be cheaper as well.



