Ah, slicksta great minds think alike A few degrees equates to a more than a few $ saved.
Good point about the doser James, I'll try not to think about that now I've spent the coin on carbon.
On the bright side, I've linked up the second lot of filters and had a play. I can get about 120 litres per hour at max flow and the Chlorine test is clear. I'll get back onto the heating issue now that my water can't dissolve fish.