The water from my faucet is very soft. GH 20ppm, total alkalinity 20ppm, carbonate 30ppm. I use one large one in my 55g and the smallest ones in my 5-7g betta tanks. I noticed drastically fewer (none now) issues with fin rot on the bettas and as you can see in the pictures, my plants, fish, and snails are thriving. The mystery, nerite, (and Malaysian trumpet) snails are breeding regularly. Their shells are very healthy too.The packaging recommends more/larger shells per gallon than what I put in, but I researched also and you don’t want to shock your aquatic life. Build up slowly. Each shell lasts between a week and a week and a half when put in a low flow area of the aquarium. I add a fresh shell after the last one is gone when I do weekly or bi-weekly water changes. 10/10!