PhotoMeter help

B

BLAKEJOHN

Active Member
I just recently purchased a Hanna HI 93713 Low range Phosphate meter. The question is....Am I supposed to multiply with the factor of .33 to obtain the value of P that we use?

Or am I to just read the display?

I think I am looking for a reading of .015

The display gives me a reading of .03 mg/l which is twice what I want. Then of course factoring gives .0099 which is better.

Which reading shall I use?
 
cbrownfish

cbrownfish

Well-Known Member
Multiply the reading by a factor of .33.

Um.....you want your PO4 to be in the .02-.03 range. Below that many corals will not do well, so .0099 is way to low to provide the proper level of Phosphorus to your corals. Especially soft corals like Zoanthids, Palythoa, Xenia, etc. IME, a reading below .02 will cause SPS to lighten up considerably.
 
fishhead

fishhead

Active Member
That instrument is only accurate to +-.04 ppm. with resolution of 0.01. Reading .015 off the scale and working with that number would be meaningless.


" the HANNA phosphate meters have been designed to cover the following ranges: - From 0.00 to 2.50 mg/L (HI 93713) 2 year warranty. Range 0.00 to 2.50 mg/L Resolution 0.01 mg/L Accuracy ±0.04 mg/L ±4% of reading Light Source LED 890 nm Light Life Life of the instrument Light Detection Silicon Photocell Battery Type / Life 1 x 9V / approx. 40 hours of continuous use; auto-off after 10 minutes of n....
 
cbrownfish

cbrownfish

Well-Known Member
fishhead said:
That instrument is only accurate to +-.04 ppm. with resolution of 0.01. Reading .015 off the scale and working with that number would be meaningless.
Click to expand...

Wrong, It is accurate to +-.04 mg/l. Look at your own copy/paste job. My note was referring to .02-.03 ppm.
 
B

BLAKEJOHN

Active Member
Thanks Cbrownfish. I thought that I needed to factor the reading from the display. What confused me was that I had no GFO or other exporsts of PO4 other than water changes and macro algae to warrent such a low reading of .0099.

I do have a mild Algae outbreak and that article shed a little light on it. Maybe the low PO4 is a contributing factor. (explains why my zoa's havent been opening well, but my GBN, Stag and Green Cap are just as bright as your avitar)

With that little bit of added knowledge I can now look at other angles to attack the algae.

Thanks again.
 
Boomer

Boomer

Reef Sanctuary's Mr. Wizard
John

Am I supposed to multiply with the factor of .33 to obtain the value of P that we use?

NO ! :D

That is only for the old Deltec/ Merck kits that use to measure Phosphate as P, i.e., P - PO4, until I got on their case. We use PO4, as does the Hanna. So, no x'ing anything.





04 mg/L = .04 ppm

Yes it does unless I want to be a tit-head about it :)

0.04 ppm x Density = mg /l

0.04 ppm x 1.023 (seawater Density, NOT Sg) = 0.04092 mg / l

Why ? ppm is a weight to weight measurement and mg / l is a weight to volume measurement. So, technically they're not the same. However, for all practicle purposes, we call them the same.

If we look at something like Ca++ and say 400 ppm it is really ~ 410 mg/l, Mg++ 1300 ppm = 1330 mg/l. So, nothing to worry about for us and what we test for.
 
Boomer

Boomer

Reef Sanctuary's Mr. Wizard
Am I supposed to multiply with the factor of .33 to obtain the value of P that we use?

I forgot here.

1 ppm P-PO4 = 1 x 3.06 = ppm 3.06 PO4

1 ppm PO4 = 1 / 3.06 = ***.3267 ppm P*** your .33

At 0.3 ppm you are at the limits of the meter.


PO4
P = 30.97

O = 15.99 x 4 = 63.96

30.97 + 63.96 = 94.93

94.93 / 30.97 = 3.06.

So, if the old Deltec kit read .23 ppm P, then .23 x 3.06 = .70 ppm PO4 Phophate ion or .23 / .33 = .70 ppm. In the P format they leave out the weight of the 4 O
 
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