The air stone is used to produce bubbles and reduce the noise level inside the aquarium. A blocked air stone usually causes a reduction in the amount of bubbles. Expect  to replace the air stone after 12 months, more frequently in harder water areas.

The mixture of air bubbles and hard water create calcium deposits that clog the pores of the air stone reducing the filtration efficiency.

INSTRUCTIONS Remove filter cartridge. Locate the air stone and pull upwards to remove. Gently push the new stone onto the one way valve stem - do not force down too far.