On Sat, 25 May 2013 08:30:21 +0000, Danny D. wrote:

From that, I can't tell if pool o-rings are buna or viton.

This pool o-ring blog implies they're EPDM (but they seem to have
their facts wrong on Buna-N so I can't really trust their advice).

http://blog.poolcenter.com/article.aspx?articleid=6082
"Swimming pool pump and filter o-rings are typically made with EPDM rubber,
while chlorinator o-rings are usually made of a Fluorocarbon, Viton or FKM.
Some more expensive types are made with a Nitrile rubber, used in Buna type o-rings."