Sorry to double post but I can't edit my last post. I didn't have time earlier to carry out a search on the NPT forum on UV sterilizers but now I've seen the thread below from Diana:
http://www.aquaticplantcentral.com/f...-diseases.html Might be good to have this as a sticky too as it's quite important. It's a mine field out there for new hobbyists and a lot of cheap chinese uv sterlizers are on sale that aren't flow adjustable.