VIVOSUN Air Stone 2PCS 4 X 2 Inch Large Air Stone Cylinder for Aquarium and Hydroponics Air Pump (2PCS 4 x 2 Inch)

I use this to keep my minnows alive here. It has enough bubbles to keep the water moving even when it’s really cold and it keeps it from freezing unless it gets in the teens or single digits. This works really well.

I use this with my PondAir 2 and they produce a nice air column.

Keeps your Fish Happy through the Winter

Nice stones work good in pond

3 of the 4 I bought worked beautifully; the fourth, I had to reseal - the air blew right out at the connection, instead of through the stone. Overall, these air stones are large, but not as effective as others I've had. I bought them to use in Koi pond moving bed bio-filters, and they will suit that purpose well.