maimz and Adam,
You want to have your water incontact with teh bubbles for as long a period of time as possible. So put your water injection fairly high up. The water flow should be slow enough to allow good contact but not too slow. There is a happy medium.
take a read of the
skimmer DIY links for some good reading.. Hopefully these will give you some answers. read the theory before looking at the design aspects. This will answer the pump size, turnover rates, how high for water injection etc.
Good reading..
[ 25 December 2001: Message edited by: DJ88 ]