Review on Pawfly Release Airstones Aquarium Hydroponics by Rachel Harris

They don't work. Just like this one. Buy something else. I was wrong in my original rating. The problem turned out to be my air hose, not the rocks. As soon as I change the tube the stones worked so I apologize to the manufacturer for the erroneous review. I assumed they were stones, but subsequent troubleshooting showed that assumption was wrong. I'm rating them 4 stars instead of 5 because they work but aren't as good as the more expensive ones I have. However, money is not a bad option. I use them for hydroponics, not for the aquarium.