Leave product inplace for 4 days, then test phosphate or silicate concentrations with either MultiTest: Phosphate or MultiTest: Silicate. If the concentration of the component you are trying to decrease has not dropped to around 0.02 mg/L, then replace the PhosGuard, otherwise leave in place until levels begin to climb again. As long as concentrations remain under control, the product is not exhausted. Over treating is not recommended. PhosGuard is not an exchange resin and does not release anything into the water. It does not leach phosphate or silicate back into the water and may be removed, dried, and returned to service until exhausted. Continuous use of small quantities is better than intermittent use of larger quantities.