Thanks chaps, i've got some reading to do I think, I may send away for another water report as I seem to have lost the old one. On South West Water's website it says that my Calcium levels are 18mg/l. Looking at getting the calcium to 150ppm it seems that I would need to add (roughly) 2 tsps of Gypsum. Just read that Calcium does indeed affect clarity, though i'm unsure why my Pilsners see to be ok. Anyway whatever, it's something to try. 
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