Product review (5 stars): It does what it advertises.
I have been using in a large 10 gallon tank humidifier and it does the job. No mildew and my wicks are a lot cleaner. However, I am curious as to why this is no longer an "add-on" item? I paid $3.98 and free ship for mine as an add-on and now it's $9.92?? I'll wait for the price to drop again and get a few extra bottles.