These filters are super easy to use and very effective. The 3 pack is the best value. They are easy to find on various websites and in pet supply stores. For my particular location, Amazon is the best place to purchase them.
This is the second time I have ordered this product from the same seller and I am quite satisfied with it. I have a ceramic fountain for my dogs (5) and it works great. I clean my fountain at least once a week and I rinse the filter in cold water at the same time to get rid of any gunk on the outside. After 30 days I replace the filter. I think this is a great product and heartily recommend it for fountains that use this type of filter.
I originally bought the Raindrop stainless fountain and filters with the idea that I would change the water less. I still change the water everyday more as a precaution. I have been using the system for about 2 months now, it works well and my cats love it which is the most important aspect.