ORP/PH correlation ?

[MarkoD]

Does anyone know if this swing is normal?

if so does anyone know the correlation between PH and ORP?

what exactly effects the ORP?

[gregzz4]

From what I tried to read on ORP, until my eyes glazed over, it is affected by many things.

http://reefkeeping.com/issues/2003-1...ture/index.php

I'm not going to use an ORP sensor