We have really humid, moldy summers in our area, and until I started this, I was emptying and scrubbing, water tanks every other day, and my tack couldn't stay in the tackroom for more than a week without getting moldy.
I love this stuff! Buy a huge bottle of mint flavored store brand stuff, splash a capful in my tanks and water buckets for scrubbing them out, and then refill. This is the most mildew free summer I've ever had in my big water tanks! I can now empty and clean the big tanks just once a week, and I'm not wasting almost an entire 70 gallons of water every other day. And I like that its not full of a lot of toxic chemicals.
It's also great to put in your tack cleaning water to kill mildew on tack. Requires a little more oiling/conditioning, but keeps my tack mold free between cleanings!