Rena Airstones

I have used them in the past, but in my experience it doesn't matter what they're made of - they plug up and put more strain on the airpump. That's probably in part due the my water, but I've given up airstones completely and just run the air through the plain tube with a lot less headache.

What do you plan to use them for?

The best airstone I have used has been a Coralife Stubby Stone made out of limestone.