I've been using them for years. They work. Tip: don't throw them away. Wash them off in tap water; soak them in a solution of white vinegar (10:1); let them dry. I now just wash them off and the same piece of wood works fine. Superglue (Gorilla) plastic case in stone for a tight seal. Connect them to your airline before loading them; run for 15-20 seconds; then put them in the water. DO NOT scratch them with a knife. Another reviewer recommended this. I tried. All it does is shorten the life of the stone by cutting away the wood. I get perfect rinsing/drying results. I have about six of these that I rotate throughout the year. I can replace one or two a year. I use them in a protein skimmer.
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