Man, y'all should try wood airstones in saltwater; even the cheapest blue airstone will outlast one of those :D
I could possibly add some info just so it's here about these and various styles. Generally though, longer lasting types are going to be in wastewater or aquaculture areas.
Molded silica - Which are the typical "colored" stones that you will find locally (blue most common color). These have the shortest life and least uniformity of bubbles, but are cheap to replace.
Bonded Silica - fused silica and then machined to shape. These are typically white and used largely in aquaculture or past wastewater plants. These have better uniformity, small bubbles and good life. Also can be cleaned. This category would also include the Alumina based diffusers too.
Ceramic plate - Actual fine pore ceramic blocks. These are always white and often used for permeation of gases into water. These have great uniformity and small bubble size. Also can be cleaned.
Flexible Membrane - These use various plastic membranes and are generally tubes. These are used often in wastewater and aquaculture. These have good uniformity and medium bubble size. Also can be cleaned.
Steel Bubble diffuser - These are heavy stainless types. The most common use for these is wastewater treatment. These have large bubbles and are aimed at circulation more than permeation. Also can be cleaned.
That at least covers the most common types used, so you can decide what you'd prefer there. Myself, I tend to go with the Bonded silica stones if I can and when I'm in a pinch I'll use the molded silica.
For cleaning. The bonded silica, alumina and ceramic plate; soak in Muratic acid for 20-30 minutes. For the flexible membranes, clean with soap and water.
(Calcium and biological sludge build up and clog pores in the diffusers which, over time, reduces bubbles. Cleaning with muratic is then required.)
hope this helps
