phosphate testing

[Johnny Reefer]

Originally Posted by Johnny Reefer

I just got a Hanna HI 93713 Phosphate low range photometer and I am confused by the readings I got from it.

For my reef tank I got 1.82mg/L.
For my FOWLR I got 2.70mg/L.
WTF? My PO4 has never been above 1.00. My FOWLR tested at that for a time in ’06.

The powder was not completely dissolved when I put the sample in the photometer. They say to shake it gently. But they also say to time it for 3 minutes once the sample is in the photometer. But I’m assuming time is of the essence, given the 3 minutes timeframe? I can’t be standing there shaking the sample hard for 10 minutes until the powder is dissolved, can I? They say not to let it stand for too long. They say nothing of ensuring the powder is fully dissolved. But they do talk about debris and bubbles throwing the reading off.
Oy vey! Yet another test kit with crappy instructions.

The leaflet says it measures PO4³ˉ. I see on Wikipedia that that’s inorganic phosphate. Okay.

The leaflet has conversions. To convert PO4³ˉ to P2O5 multiply reading by 1.49.
To convert PO4³ˉ to P multiply reading by 0.33.

I have been using the Elos PO4 kit for testing up to now. I should state that I do not read this test exactly as directed by Elos. They say to look down at the sample through the top of the vial. I have always looked from the side, as this is how other test kits are.

Latest readings with Elos was yesterday.
Reef: < 0.1
FOWLR: 0.1

If I convert my Hanna readings to P, I get.
Reef: 1.82 x .33 = 0.6006 mg/L. This is more like it!
FOWLR: 2.7 x .33 = 0.891. Again, more like it!

I don’t get what I’m missing here.

I’m assuming P is organic phosphate? Maybe I should just be happy with the converted readings I get of that? I have read/heard that organic phosphate is the more important phosphate to keep tabs on anyway?

Sorry. This chemistry business is one of my weaker aspects of the hobby.

Anyone with any experience or light that could be shed on this would be greatly appreciated.

Thanx much,

Bump.

[marie]

I'm one of those ostrich people (I keep my head buried in the sand ) If everything is going good then what I don't know won't hurt me. It's working so far and I do keep a very close eye on the animals to make sure nobody is off colour or unhappy

The only thing I've tested for in the last 6 months has been alk (If my alk drops I assume my cal is dropping too)

I've even given up testing Mg, If the coraline stops growing on the glass then I add a few cup fulls

[fkshiu]

I'm with Marie. I don't remember the last time I tested for phosphates or nitrates or even pH. I test for Ca, Mg and Alk maybe once a month. I usually use the state of my livestock as a measure of my levels.

[awa1979]

I dont test for phosphates, I dont have an algae issue and everything is happy and growing.

Not to mention API kit records 1.0ppm sometimes 2.0ppm but the Elos kit shows no phosphate every time.

So one of them is off.

[Delphinus]

I gave up on the Hanna photometer altogether, found it a very cumbersome way to test.

Never could get the powder to dissolve. I both called and emailed Hanna Instruments about this, they didn't really have anything profound to say about it (they basically read the instructions to me). Although I did finally get someone who said that's why you have the 3 minute timed reading, to allow the undissolved powder to settle.

Thing that really drove me nuts is I couldn't get consistent readings from it. But then I was getting way lower numbers than what you got, I'm surprised, you definitely seem to have unbound PO4 in your water.

I think, FWIW, the tester is better for measuring trends in the 0.x range (not 0.0x range like some people on RC were claiming. "Oh I added Rowaphos and my PO4 went from 0.08 to 0.06!" ... IMO those people aren't using the tester correctly. With a potential error of plus/minus 0.04, the only real significant digit interpretation is going to be in the tenths not the hundredths. Again IMO.) I think trending is probably more useful than understanding whether it's P or PO4/3- or P or P205... I don't know, that whole phosphate stuff is getting kind of low level chemistry if you ask me, I didn't quite get that part either.

Good luck sorting it out.

[buddyreefer]

i hate testing with kits, so frustrating as there is so much variations with everything, i am now a firm believer in 20 percent water changes a week. i just have pumps all setup so its a breeze don't understand why people hate changing water so much its pretty routine and only takes half an hour as long as you've had some sw mixed up in the garage. I do dose 2 part tho. and i take my water to the lfs for testing if something seems amiss.

[chevyjaxon]

Originally Posted by buddyreefer

i hate testing with kits, so frustrating as there is so much variations with everything, i am now a firm believer in 20 percent water changes a week. i just have pumps all setup so its a breeze don't understand why people hate changing water so much its pretty routine and only takes half an hour as long as you've had some sw mixed up in the garage. I do dose 2 part tho. and i take my water to the lfs for testing if something seems amiss.

+1

ALL test kits suck i hate them i never use them i just watch my ph and fly by the seat of my pants too many variables with all test kits i like my pinpoint ph monitor period