phosphorus standard

[reefkeeper2]

Anyone know where I can get a low range phosphorus standard? I want to check the accuracy of my photometer.

[Randy Holmes-Farley]

I've had to make them myself, but perhaps others have some ideas. It would be especially useful for it to be in seawater, otherwise it is not an especially good test.

[reefkeeper2]

Wow, I see a new line of future reef products. Randys Standards.

[Randy Holmes-Farley]

It would be nice for someone to sell such products.

[reefkeeper2]

I tested for PO4 yesterday and got a reading of 0.05. I changed the GFO four days before that. Today I tested and I got a reading of 0.0. I suppose this is possible, but I wonder how accurate that reading is. (I did it 3 times) .

[Randy Holmes-Farley]

I do not know how accurate it is either, but enough GFO can pull the phosphate down fairly quickly.

[m2434]

I would think you would be able to find a standard through an industrial supply co.

Is this is the
low-range Hanna photometer? If I remember correctly, the manufacture claims it is accurate to .04mg/L or 15% of the reading - whichever is larger.

So your PO4 should have gone down by at least .01mg/L

[Randy Holmes-Farley]

It is easy enough to get standards, just not in seawater. Here's one from Cole Parmer (they have many):

http://www.coleparmer.com/catalog/pr...sp?sku=8697450

[reefkeeper2]

I have the milwaukee photometer. Since you zero the instrument with the liquid your going to test before you add reagent, why is it important to have a seawater standard? Is it the reagent?

[Randy Holmes-Farley]

Other ingredients in seawater may react with the reagents, or prevent the reaction of phosphate with the reagents in ways that alter the result, either upward or downward.