I have used Spa Cuzn for 3 years or more in my 300 gallon hot tub and love it! It keeps my water clear, it doesn't involve any plastic (I special order it without the pipe piece they supply to prevent product getting sucked into the system) and no chlorine. It lasts 4 - 5 months - maybe uses copper? - without any additional sanitizing than a small weekly dose of potassium monopersulfate shock. I'm in love with this product and want help figuring out if I should be concerned about using it. Best thing - zero testing required during the 3-5 months except at startup to initially balance the water. I highly recommend in terms of it working fantastically.