Product review (5 stars): This filter is effective but expensive for the amount of time it lasts when using it nightly.
Because I have severely dry eyes, I need a humidifier in my bedroom and use the filter with it. I wish the filter lasted longer than it does and it seems too expensive for what it is. I have used one filter since then and it is now brown enough to use the second filter I purchased. They are not available locally. .Thank you  for asking.