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View Full Version : What PO4 test works!!!!!???????


wickedfish
12/07/2010, 11:49 AM
Alright someone out there must tell me what test actually reads closer to the truth:confused:

I started by opening up my new hanna phosphate checker, read all instructions and tested my water this morning. .13 PO4 according to the hanna checker. Its the green mini one. Also tested my water source .05 and the tds is 0.

Then I did the salifert test non expired. It read closer to .03 than 0 but not 100% clear it had no tinge of blue but was cloudy a tiny bit.

Elos which I think is probably not a good one since I know there is phosphates present, reads flat out 0. How do I know there is phosphates present...my chaettomorphia grows like a weed and is lush green, which leads me to believe there is plenty of phosphates.

Cliff, Boomer, Bertoni and all other Chemistry studs what do I trust? What is closer to an honest test for PO4? :spin1:

I read in another thread someone was saying there water was reading .03 on the checker after the tds was 0. Can there be flaws in this checker???

And thank you for your valued answers!!

Allmost
12/07/2010, 12:02 PM
Im interested in this as well, and I have just given up testing for po4 and no3 ... I just look at my corals and how they look and go by that.

from Hanna po4 checkers :
"Adaptation of Standard Method 4500-P E Accuracy 4% ±0.04 ppm (mg/L) of reading 0.04 ppm (mg/L) resolution (250 points) Large, easy to read digits Auto shut-off."

so reading of 0.03 PPM could be zero, or 0.07 PPM ... .

so Hanna reads 0.13 for tank water, salifert at 0.03 and elos at 0 ? or are those for the source water ?

does the checker work the same way in seawater and freshwater ?

meshwheel
12/07/2010, 12:20 PM
I do not consider myself a chemistry stud, but reagent grade Phosphate test kits are not very accurate!
Get yourself a Hanna phosphate checker for 50.00 and get a much better reading!!!! Down to .00 levels!
I use one and they work great!!

HighlandReefer
12/07/2010, 12:51 PM
IME, the Salifert Test kit is good to let you know if your phosphate is below 0.3 ppm when comparing it to the more expensive Hach PO-19 phosphate kit. As far a accuracy with phosphate levels below 0.03 I don't believe any of the kits or meters are all that accurate. There are too many interfering factors found in marine tanks.

If you have two kits that appear to read zero, then I would assume your phosphate level is at 0.03 or below.

If you are concerned about pest algae or other organisms, then I would continue to run GFO and replace it as needed to maintain as low a phosphate levels as possible.

wickedfish
12/07/2010, 01:20 PM
Meshwheel that is the checker I used.

Cliff, thank you. I am currently using gfo replaced every 6 days and gac replaced every 4. I have o pest algae for the past week. Thank goodness. But still would like the phosphates to be 0 and stick. I will look into a better way of measuring po4.

UVvis
12/07/2010, 02:55 PM
Standard methods 4500-P E is the ascorbic acid method. From Standard Methods, the ammonium molybdate and potassium antimonyl tartrate react in an acidic environment with the orthophos to make phosphomolybdic acid, which is reduced by the ascorbic acid. The molybdenum blue is read at 880nm.

Interferences are arsenates, hexavalent chromium, and nitrites are know to interfer. With this method, and a spectrophotometer with long light path, you can get down into the ppb range, I've had detection limits down to 3ppb (.003mg/L-ish). The method should relatively free of matrix effects from salt/freshwater.

For this method, there are a few things that you really have to watch for.

If your water has a very high alkalinity, you will need to add more acid (usually in the first reagent mix) to get the reaction going. From there, the reaction takes time a while to develop. Contamination can give high readings and honestly can come from residue from some detergent soaps on your hands.

Now, here is the kicker. To get good results, you need a non-biased measuring device (photometer, spectrophotometer) and the longest path cell length you can get for lower levels of measurement. Most test vials are 1cm path range, which already puts you on limits for the amount of detection you can get.


In all honesty, and with my full bias as an analytical chemist that has probably performed hundreds of thousands of this analysis, these orthophosphate test kits are really a 'best guess' approach. To be sure of your number, you would have to make/buy a range of standards, and test your measuring device to be sure your numbers are accurate. From there, you would have to spike your sample with a known concentration of phosphate to be sure that your matrix is allowing full recovery.

I don't expect everyone to go out and buy full scale lab equipment, but you have to look realistically at the values. With droppers and vials using a human eye, your precision and accuracy are not all that great.

Maybe I should go into buisness making standards for folks to check their test kits.

wickedfish
12/07/2010, 04:29 PM
I'm sure if you refined it you would make a million easy.
I think the main thing is we need a strictly marine/reef phosphate meter. And for it to measure in and around the 0's. And for the darn thing to be the real amount.

I hear you when you say we can foul up the test by 100's of ways. I imagine if your like me you always do 2 to make sure and cross check with other brands as I often do.

I am confused....

wickedfish
12/07/2010, 04:52 PM
Allmost,

Those numbers are for the aquarium. But I also tested my 0 Tds ro water with the checker and it says it reads .05, anyone else get high numbers with this checker?

sbreefer
12/07/2010, 05:02 PM
guys FWIW... I send my water to aquarium water testing.com about once a month. They check 15 params using spectrometry. WAAAYYY more accurate than any kit can deliver. they are in Loveland, CO a division of aquamedic. I only use my kits (or checker) to gice me a rough idea if something looks very amiss.

HighlandReefer
12/07/2010, 05:22 PM
The test results from AWT leave a lot to be desired from many posts I've seen in this forum. In many cases duplicate samples have been sent in with varying results. ;)

HighlandReefer
12/07/2010, 05:36 PM
UVvis sums up the accuracy of these meters and test kits when he stated:

"In all honesty, and with my full bias as an analytical chemist that has probably performed hundreds of thousands of this analysis, these orthophosphate test kits are really a 'best guess' approach. To be sure of your number, you would have to make/buy a range of standards, and test your measuring device to be sure your numbers are accurate. From there, you would have to spike your sample with a known concentration of phosphate to be sure that your matrix is allowing full recovery."

The hobby grade test kits & meters are not going to give you the accuracy you want. ;)

sbreefer
12/07/2010, 05:39 PM
highland, That is interesting. That is the first I have heard of the that. They still use superior methods than us reefers really have access to.

wickedfish
12/07/2010, 06:50 PM
Cliff,

Brutally honest as usual, thank you.

bertoni
12/08/2010, 01:33 AM
The Hach test has been evaluated and is accurate enough for our purposes. IME, the Salifert test kit is close, too, although it's a bit harder to get a number without the color wheel.

The Hanna photometers come in three models. Two are only accurate within 0.04 ppm at the low end. The other might be more accurate, but it hasn't been out long enough for me to trust it yet.

bertoni
12/08/2010, 01:33 AM
The Hach test has been evaluated and is accurate enough for our purposes. IME, the Salifert test kit is close, too, although it's a bit harder to get a number without the color wheel.

The Hanna photometers come in three models. Two are only accurate within 0.04 ppm at the low end. The other might be more accurate, but it hasn't been out long enough for me to trust it yet.

Personally, I trust the Hach the most so far.

HighlandReefer
12/08/2010, 07:56 AM
Cliff,

Brutally honest as usual, thank you.

Your welcome. ;)

The testing equipment used by chemists to detect low levels of phosphate found in the ocean is much more expensive than most of us can afford. The procedures are much more involved, require much more time & require training to acquire accurate results. UvVis has only hinted at this aspect regarding his statement above.

Luckily we hobbyists do have a fairly large range to work with regarding phosphate levels in a reef aquarium.

Pristine reefs average around 5 ppb. From research as well as what hobbyists have stated here on RC, it seems that coral do well with phosphate levels up to around 200 ppb. With hobby grade test equipment, the best we can hope for is to determine if our tank phosphate levels are below 30 ppb, perhaps a stretch would be down to 10-20 ppb. Still short of the 5 ppb.

Most of the algae pest species we seem to have problems with are found in the pristine reefs (5 ppb). So this should say something to you regarding controlling these algae pest species. Coral & other beneficial organisms need phosphate as well. For many species of pest algae, lowering phosphate levels alone is not going to control them. You need to remove them from your tank, like weeding a garden. If you lower the phosphate level low enough to kill these pest algae, the coral will die as well.

Research has found that algae species tend to increase their growth rate as phosphate rises. Many hobbyists have made statements, including myself, that one can watch the rate of algae growth on their tank glass. Using hobby grade test kits, the goal is to get your phosphate level to be undetectable. Notice I use the word undetectable and not zero. When hobby grade test equipement read zero, that simply means this kit or meter can't detect the lower levels of phosphate present. From their, the best phosphate test kit I have found is watching the rate of algae growth on your tank glass. This method seems to work well for many hobbyists & I don't believe you are going to find a better hobby grade method for judging low phosphate levels in a reef tank. :)

UVvis
12/08/2010, 08:19 AM
The test results from AWT leave a lot to be desired from many posts I've seen in this forum. In many cases duplicate samples have been sent in with varying results. ;)

For this analysis, samples need to filtered as soon as possible. Particulate phosphorus will be degraded into more PO4, depending on bacteria, sample temperatures, lots of factors. Sample submission containers need to be acid washed (I prefer overnight in a 5% nitric bath) fairly well too.

The sample hold time isn't great for this one. It also depends if you want to fraction the phosphorus containing compounds by particulate/free. There are also methods for digestions to convert almost all phosphorus to phosphates for total P counts.

EddieJ
12/08/2010, 08:37 AM
I use the Hach Colorimeter II with the PhosVer 3 reagent. very consistent results. I basically use it to determine when my GFO is exhausted as I see the #'s creeping up from .03. Like it has been said before, nothing replaces observation of your tank and experience. I think too many reefers get caught up in the #'s and miss what is happening in plain sight.

HighlandReefer
12/08/2010, 09:29 AM
For this analysis, samples need to filtered as soon as possible. Particulate phosphorus will be degraded into more PO4, depending on bacteria, sample temperatures, lots of factors. Sample submission containers need to be acid washed (I prefer overnight in a 5% nitric bath) fairly well too.

The sample hold time isn't great for this one. It also depends if you want to fraction the phosphorus containing compounds by particulate/free. There are also methods for digestions to convert almost all phosphorus to phosphates for total P counts.

The Hach PO-24 Total Phosphate kit is availabe at a price of $148.00 USD. I have not seen any data for what the suggested levels one should shoot for in reef aquariums. Do you have any figures regarding this?

lj1064a
12/08/2010, 10:31 AM
What model Hach kit are you referring too? I have one of the hanna meters and would like someting to compare it with. Right now I am using the AP kit mainly due to the ease, but would like something a little more accurate.

thanks

lj

d0ughb0y
12/08/2010, 11:01 AM
I used a Milwaukee low range photometer before and I think it is quite accurate.But I did notice that while I had 0 readings, I only need to clean my glass of algae every 6-7 days and when I have phosphate readings, I need to clean every 1-2 days (or at least more frequent than once a week). So I sold the photometer and just use algae on glass as my indicator. I also tested phosphate while using GFO and observed the GFO can quickly bring down phosphate in 1-2 days, fastest probably during the first 8 hours.

HighlandReefer
12/08/2010, 11:02 AM
What model Hach kit are you referring too? I have one of the hanna meters and would like someting to compare it with. Right now I am using the AP kit mainly due to the ease, but would like something a little more accurate.

thanks

lj



Jon is refereing to the Hach PO-19 kit sold at www.hach.com for around $90.00. Refills are much cheaper once your purchase the equipment provided in the kit. ;)

Randy recommends this kit after he tested it. :)

UVvis
12/08/2010, 11:24 AM
The Hach PO-24 Total Phosphate kit is availabe at a price of $148.00 USD. I have not seen any data for what the suggested levels one should shoot for in reef aquariums. Do you have any figures regarding this?

.03mg/L and lower is supposed to retard algae growth. For a target, value, there is a big 'it depends' factor. For example, Waikiki Aquarium had a paper out in 1995 about coral growth in their high inorganic nutrient, low organic nutrient, low pH salt water well. I'll try to dig that up. Anyway, they had PO4 counts in the .05 to .06 mg/L range and had years of great hermatypic coral growth. The values of organic C:N:P were much lower than seawater and standard tanks though.

Not that I'm trying to be illusive, but from everything I've seen on the issue, optimal levels seem to vary somewhat system to system in relation to the animals, and the individual body of water.

HighlandReefer
12/08/2010, 11:42 AM
.03mg/L and lower is supposed to retard algae growth.

Are you refering to total P or phosphate here?

bertoni
12/08/2010, 12:49 PM
Yes, Cliff is correct, I've used the Hach PO-19, and it seems very good. The total phosphate kit is interesting, but very pricey and a bit tedious to use.

UVvis
12/08/2010, 01:06 PM
Are you refering to total P or phosphate here?

Sorry, .03mg/L for the free phosphate ion.

Total Phosphorous numbers have less meaning without analyzing for total carbon and total nitrogen for stoichiometeric reasons. The sample prep will vary the meaning of a phosphorous digestion as well (particlate, non particulate, organic...)

HighlandReefer
12/08/2010, 01:10 PM
Thanks, I appreciate your take on Total P. ;)

wickedfish
12/08/2010, 03:47 PM
Gonna have to add Uvvis to the list of chemistry studs. Thank you for the replies everyone.