I have the ULR Phosphorus meter and find it very accurate. I did some experimenting around on it's accuracy. I diluted the water I was testing with P-free seawater and found it gave bang on results.
One thing about the alk-meter I just read is that they had reliability issues with the powder reagents and are replacing them with liquid:
http://reefbuilders.com/2011/01/24/h...placed-liquid/
For alk, Ca and Mg, the ordinary test kits (i.e. Salifert) are accurate enough for my needs.
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180 gal tank, 50 gal sump, PM RFCa6 Ca Reactor, SWC Extreme 250 1A Cone Skimmer, Tunz Osmolator ATOF, Aquacontroller Apex, Aquaillumination Sol Super Blue 6 x 75w Units, Acros/Softies/LPS/Mushrooms/Zoos, Purple/Powder Blue/Yellow Tang/3xBlue Chromis/2xTomato Clown/Lawnmower Blenny
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