Air stones are a great way of adding motion to your tank and circulating the water. It also replenishes oxygen supplies improving the water quality and helps to release carbon dioxide which may build up and be harmful to your pets. It is best to get a long stretch of tubing which can be run under your substrate to hide the tube and ensure your tank has a more natural feel as the bubbles rise from the airstone.
Remember you will need to buy an air pump separately.

 
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2x Air-stones / tubing

Small disc air-stone

 

Air-stone, non-return valve

 

Air pump non-return valve