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Re: Phosphate Test Kit

>I've been using a Seachem Phosphate Test Kit for about a year now. Before I
>started dosing KH2PO4, the phosphate level was so low (~ 0.1 mg/l) that I
>didn't think much about it.  But now, on Tom Barr's advice, I'm trying to
>keep the level at 0.5 mg/l.  And, lately, I've begun to doubt the results of
>the test.  This morning, I tested the reference solution that comes with the
>kit and, instead of getting the 1.0 mg/l I should have, I got about half
>So, my questions are: Do the reagents "expire" in as little as a year, or is
>this test kit inherently inaccurate?  If the latter, does anyone have an
>opinion on which of the more expensive Hach or Lamotte kits would be better?

With the phosphate kit it is very, very , very important that exactly 
one full stem of sample be used. A little bit more or less will throw 
off the color. Also, take the reading between 10-30 seconds as the 
color does shift off scale the longer it sits. If the cap on 
phosphate reagent#1 has not been on or has been kept loose then the 
reagent can evaporate slightly and this will also alter the test 
result (normally not a problem but I mention it because very old 
phosphate kits won't work because of this i.e. 5+ years).

Gregory Morin, Ph.D.  ~~~~~~~Research Director~~~~~~~~~~~~~~
Seachem Laboratories, Inc.      www.seachem.com     888-SEACHEM