We have consistently used this product for the entire summer of 2014. We use a Drinkwell fountain and these packets fit perfectly behind the filter. This is a great product that really does work well. We change this packet out on the 1st of every month. On July 5th we noticed a couple marks in our lawn and realized we hadn't changed it out several days earlier. Put a reminder on your phone or calendar because it is that quick that the marks reappear. Excellent product and will continue using.