Product review (5 stars): No Metal - No Corrosion - These are Great!
I really like these filters; there's no metal in them. We have a water softener and have always used potassium. Last winter we had a hard time finding the potassium and had to switch to salt. The salt ate up the metal inside the WF813 filters and we had a hard time with green corrosion in our humidifiers. I am very happy with these disposable filters and highly recommend them. It is suggested to replace them monthly and the quality looks like each filter could last a month.