Mineral Algaecide Unit, up to 6-Month Algae Control, for 100-400 gallons, Yellow & White, New Formula with Silver.

We switched from bromine to Chlorine after using one in our pool was such a impressive change. My skin feels so much better than when i got in the spa with bromine it really helps keep our spa cleaner, and the water FEELS cleaner

Working great in a large fountain!!

Really helped with chemical balance. The only thing I had to add all summer was salt occasionally and chlorine shock.

Worked very well and I'd definitely use it in the future.

This is a great product for keeping the hot tub clean, clear, and non gritty.

We keep these on hand for our hot tub. Has kept that stagnant water odor and slimy feel away for sure. We will always use this product for our hot tub. Easy to use and doesn’t bother my sensitive skin.

Have used these for a while now. Works like it says.

As other reviewers experienced, this IMMEDIATELY turned my hot tub water green, and left a green ring at the top of my hot tub (see photo). I decided to give this item a try during a standard purge / drain / clean / replace filter with a brand-new unit / refill hot tub maintenance period. After bringing the hot tub up to temperature, and pH, alkalinity, etc. into spec, I popped this unit into my hot tub's strainer basket, and turned on the jets to full to introduce this item's minerals into my water. Immediately, and right before my eyes, my water turned green and got darker and darker green as the 15-minute jet cycle completed. It also left a green / blue ring at the hot tub's water line. This color didn't clear up at all, so I had little choice but to drain and refill my hot tub again. The water has remained non-green since then, but hasn't been any clearer than it was before nor has this enabled me to use any less sanitizer. The only things this unit seem to do is impart a mild unpleasant smell to the water (similar to other copper-based items I've tried - smells like crayons), and regularly deposit a faint green ring at the hot tub water line. This doesn't seem to do anything beneficial at all.