Air stones last about six months before they become clogged. Some people use small cheap air stones that can be bought for fifty cents on Amazon. Recycling these is ridiculous. But some people like the expensive air stones ($5 to $20). It can pay to save these till some reasonable quantity are accumulated. Then clean them.
Don’t simply throw them in acid. These stones are clogged by both protein and water-hardness compounds. The protein is much like the tarter on your teeth, very tenacious and tough. Protein is removed by lye, not acid. To remove these deposits, do the following:
- Soak in concentrated lye (sodium hydroxide) for one week
- Soak in plain water for one day
- Soak in concentrated hydrochloric acid (pool acid) for one week
- Soak in water with some baking soda in it for one day
This will make the stones like new. Note this won’t work on polymer wands or wood air stones.
Note also that lye and acid are dangerous. Use eye goggles and rubber gloves when handling them. Lye and acid can be obtained from your local hardware store. The concentrations should be the hydrochloric just as it comes and a fully saturated solution of sodium hydroxide “pearls”. Only really strong solutions work well.
Source: Aquariumscience.org – David Bogert