cheap phosphate test kits

To: Aquatic-Plants at actwin_com
Subject: cheap phosphate test kits
From: Craig Bingman <cbingman at netcom_com>
Date: Mon, 17 Feb 1997 02:29:21 -0800 (PST)
In-Reply-To: <199702150839.DAA01078 at looney_actwin.com>


> >Hi, can someone give me a quick answer on whether or not the Seachem Test
> >Kits are reliable for freshwater? I need a phosphate test kit and the
> >Seachem is quite a bit cheaper than the LaMotte. I can order one from my
> >local store if I put in a request by tomorrow but I'd rather spring for
> >the LaMotte than get a test kit that isn't accuarate. How about the iron
> >test kit?
> 
> I have been pleased with SeaChem's test kits, and particularly so with the
> phosphate kit.  

While the SeaChem test kit should read just fine in fresh water, it is 
not nearly as sensitive as the packaging indicates.  You will have 
difficulties detecting phosphate at < 0.1 mg/L, and perhaps slightly 
higher values.  The problem is twofold.  The strong yellow color of the 
tungstomolybdic acid visually masks slight amounts of blue/green color 
from the phosphomolybdate complex, and the path length is not great 
enough.  

At present, I would rec the Hach low range phosphate test kit (PO-19) for 
anyone who really wants to look at trace phosphate.  It is forty dollars, 
and although that is more than $15, you get what you pay for in this case.
 
Craig