testing for phosphate

[foxhuntr]

Ok all you stick fans......what do you use to test your phosphate ? I used a hanna 713 , elos and a salifort ...they all come up with different readings......the hanna i did 3 times in a row and came up with 3 different readings i got .09 ppm, .34 ppm and .03 ppm......which do you go by.....thinking about trying a hanna 736 which reads in ppb which is suppost to be more accurate.....what does everyone else think ? ....need some input

 

[143MPCo]

I have a Hanna, one thing I do to aid in consistent readings is clean the test vial after every use with a qtip and RO/DI water... Then I rinse vial out with some of the extra sample water to be tested, seem to help for me.

 

[foxhuntr]

Yeah....i do the same...i rinse mine with rodi water then i rinse it 3 times with test water and then i wipe it clean with a soft cloth before putting it in the reader and still get different readings every time .....there has to be something more accurate out there.....i can see if the readings are real close but from .34 ppm to .03 ppm ? Thats a big difference

 

[UK_Pete]

Bubbles and fingerprints affect the hanna I find- took me a while to get consistant readings with it but I seem to have got it now and get pretty repeatable readings:

https://www.reef2reef.com/forums/re...ey/189672-phosphate-question.html#post2180792

BTW soaps and washing liquids can contain phosphate, keep them well away, never use on the bottles, and don't contaminate the sample water with soap residues from your hand when you take the samples. I also use a technique I read about which is put the bottles in the tank upside down, and turn them over once they are fully submerged, so you dont sample the surface film of the water in the sample. Also if you are getting 0.3 with the hanna, you should be able to see a fairly blue color in the vial with the naked eye. If your different readings are the same color to the eye but the hanna reads them differently (like 0.3 compared to 0.03), suspect bubbles, dirt, fingerprints, dirty LED or light photodiode in the hanna etc. Maybe do the test 3 times again but save the liquid after you test it each time in 3 shot glasses. Compare with the eye. If the hanna reads them differently but they look identical then you have a clue that the hanna is not reading them right.

 

[foxhuntr]

How can you clean the light photodiode ? I really make sure the vials are nice and clean and after i put the regent in i let it rest for a couple minutes to make sure all the micro-bubbles are out and then i wipe the vial off with a cloth and then i test it for 3 minutes

 

[foxhuntr]

UK_pete .....are you using the 713 or the 736 hanna ?

 

[UK_Pete]

@Foxhunt yup using 713 too. Although I think the only difference is the software, I'm pretty sure I read some forum posts where people were discussing that they use (or can use) the same reagent, but they display the results differently.

I've not sure you can clean the 2 diodes, when you take the battery screw out, if you open the top of the case then as if you are putting a vial in, the insides are free to come out. Theres a little electronic board with the 2 diodes on each side of the plastic vial tube. I couldent see a way to get them off without risking damage so I am just hyper careful to only put really clean vials in, and keep the thing closed when not in use. Putting a wet vial with saltwater on it could easily get a drop on the LED which is really close to the vial, and might even ruin the meter (not sure if hanna would replace it in this situation).

As described in the other thread I cap and then wash the vials, then just before putting each one in, I buff it with a new tissue. Maybe a cloth would be better as its lint free and lint might get on the diodes and screw the readings (permanently!). The meter is only looking through the vial at one point (side to side), so anything that obscures that view will mess with the readings. Dirt on a diode might be the same each time, so would not affect the readings, but I would not bet on it. Of the utmost importance though, is that the sides of the vial are utterly clean and polished - any smudge will diffuse the light and significantly reduce how much light the photodiode, on the other side of the tube, gets.

If the first (sachet free) vial is clean, and the second (with sachet added) vial is smudged, you will get a high phosphate reading. If its the other way round, you will get a low reading. The glass needs to be really shiny so if you look at a reflection in it, the reflection is perfect around the middle bit of the vial (top and bottom dont matter). Also, any bubbles, specially microbubbles or cloudiness, will totally screw the reading, so don't shake it too vigorously. If its cloudy you have to wait till its settled (use the other vial to do reading C1 with fresh tank water in this case - cleaned very well again). If it wont go to a completely clear and or blue tinted clear color, theres something wrong.

Its annoying not getting repeatable readings I know! Try the thing with the shot glass as I said.

 

[foxhuntr]

Thank you UK_Pete........i seems that i am doing everything the same way as you other than rinsing the vial...... maybe my vials need dipped in acid or something to clean better.......or maybe i will order some new vials and try that

 

[ultimatemj]

I use the 713 and I noticed variabilty until the reagent is completely disolved.
If you put the reagent in after it says C2, there is a bit of a "rush" to get it back in and get a result....then retest and it's very different.

I've shifted to using both vials, one just with tank water and the other with tank water and reagent.
Once the reagent is disolved, then I start the process of zeroing the hanna, putting C1 in, and then thefully disolved for C2.

This way also allows you to "remeasure" multiple times without remixing reagent....just rezero, but the clean vile in again for C1 and then the mixed vile.

Now I get measurements within the published gage error range of 0.05, and with the multiple measurements I can better understand "the middle" of the measurements. Considering this is just measuring the P04 in the water, I'm comfortable with this method

 

[tonizzy22]

I use hanna 713 and reading are always the consistent for me. I do clean the vials with rodi water and rinse with tank water before each test.

 

[UK_Pete]

@Ultimate - same for me. Thats why I shifted to the 2 vial method too. Much better and you can repeat the check a few times, rotating the vial each time (different from rerunning the test, which means a new sachet each time). If phosphates are low, from what I understand and my limited experience, the whole sachet dosent have to dissolve BTW - thats also what hanna told an aquarist who queried it with them. If phosphates are high, you might need the whole sachet to fully develop the dark blue color.

@Fox, I wouldent order new vials unless yours are scratched. If you have no decent mineral acids (hydrochloric, sulfuric, nitric) then try descaler (for kettles). Just on the glass vials, not the caps. Dissolve it in a saucepan of water (not too much water - an inch about), and then immerse the 2 vials in the water so they are covered. Make sure they are full of descaler water liquid. Boil them for a bit, then leave them for another 30 mins in the liquid, then rinse them many times (like 10 or 20 times, inside too). Then try. I think that should remove calcium carbonate buildup pretty well. Not sure about organic build up but it probably helps that too. If your vials still dont look brand new, like they are direct from the factory, then you probably wont get good results still.

Another thing to try is do a test without a sachet of power in it. It should come out zero.

And as I say the easiest test if you are seeing 0.03, then 0.3 - that type of range - is visually look at the liquid of each test (the one with the sachet in it). Save it for 3 tests in a row and compare. Do this within half an hour though because I read that the color can fade in a few hours. You can easily see the difference between 0.3 and 0.03 with the eye.

 

[markak]

UK pete.... am I to test tank water or Ro water without sachet of powder to get a zero?

 

[UK_Pete]

Mark - use tank water IMO, I mean, this test is not telling you that much apart from, it dosent cost anything (no sachets), and it lets you know if your technique or vials are bad. You can do it many times to check your technique and practice it too. If you fill the 2 vials with tank water, add no sachets, and do the test as if you were using sachets (including the shaking), then if you get a reading thats not zero, you KNOW youre doing something wrong, or your vials are bad etc. It could be too much shaking making microbubbles, or finger prints on the vials etc, but something is wrong because the sachets produce a blue color in the presence of phosphate that the meter can 'see' (it shines green light through the blue liquid and so the blue liquid reduces the transmission of green light, the amount of 'reduction' is the ppm phosphate). If theres no sachet, theres no blue, and if the water in test C1 and C2 is the same (whether its tank water, or RO), but you have a reading, then something about the technique or equipment is wrong.

I don't want to suggest I am an expert with this test, but I did tinker for weeks when I first got it, until I was happy with the result. Recently I've been doing several tests a day for various reasons. I've got through over a hundred sachets since I got the meter, need to order more now (I'm actually spending too much so I am trying to use my own chemicals to save money). I also read up on how it works, and that helped. If you understand what the meter is looking for, you will easily see what can interfere with that result. I also found that practice helped getting really consistent results. When you are very clean with your technique and do things exactly the same each time, consistency improves. This test is at the edge of the technical ability of phosphate testing without getting far more complex, but you have to be a bit professional in how you use it if youre measuring very low levels.

A few things that might mess tests up:
The water in the vials should never touch your fingers, or anything apart from the vials (never put your finger over the top of the vial for instance).
The rim of the vial should never touch your fingers (fingers might have phosphates absorbed on the skin, or dust etc).
The sample of water should be taken from under water, so that you don't 'skim' the surface of the tank water when you take the sample.
Personally I take the sample in an area of flow where the water that flows past my fingers does not go into the tube (ie take the sample with the vial underwater in the direct flow of a pump, pointing towards the pump).
The vials should be capped immediately, and then (still capped) rinsed under the tap IMO (to get rid of salt, prevent it getting onto the checker light diodes, and make sure the glass is clean).
The vials must be clean and the caps too. I store them with the caps tight on so they stay wet inside to prevent deposits forming, I rinse them with tap water after use several times with a final RO rinse, and I rinse them several times before using them (last rinse in RO). I do the same with the caps. It does take me a good few minutes to do a test from start to end.
I think that rinsing with tank water is good too - when ready to take a sample, I fill the vials, then empty them back to the tank. Do the same again. Last time I do this, I dont empty them back to the tank - thats my sample water.

Once the vials are full, washed with tap water and dried, I remove one cap, pour a sachet in it, cap it again, rinse it under the tap again, and dry it again. Then I start to shake it. I shake it for 2 mins by the clock. Then I put it down on its base, take the other vial (with no powder in it), clean it very carefully until its perfectly shiny (dry buffing it, I use a tissue but maybe a clean, lint free cloth would be better), put it in the checker without touching the glass, holding it by the cap, and close the checker, zero it (C1), take that (blank) vial out, clean the other vial in the same way, put it in the machine and close it, hold the button down so the countdown starts, and sit back for 3 minutes. A the end of that 3 mins, the reading is ready.

I also visually check before putting either vial in the machine, that the liquid, whatever color it is, is perfectly clear. Any turbidity at all will mess the test right up. Its got to look like diamond or sapphire - really sparkling clear. If your tank water is not clear enough for that, I don't know if the test will work well for you. The professional version of this test requires filtering the sample if its at all turbid.

My hanna 713 ritual is almost superstitious, but I also got screwy results at first, and this ritual is the result of my experiences. Much of it is probably unnecessary but I don't think any of it will detract from accuracy, just waste your time, so you can always try missing steps out. I had very low phosphates at the time which magnifies slight differences in technique. I retested the same vials multiple times and got 0.03, 0.00 etc (no new sachet, just putting vials back in machine etc) which is where I learn about clean vials. With ultra clean everything I pretty much don't get this variation.

These 3 links are lab instructions, and the hach instructions, for phosphate testing using a similar or identical chemical technique. They are interesting also to get a handle on the aspects of the procedure that the professionals use.

http://water.epa.gov/scitech/methods/cwa/bioindicators/upload/2007_07_10_methods_method_365_3.pdf

https://www.uvm.edu/bwrl/lab_docs/protocols/OrthoP_Lachat.pdf

www.[B]hach[/B].com/asset-get.download.jsa?id=7639982670

 

[swk]

My favorite po4 test I've tried so far is the Elos professional low range po4 kit. I prefer it to either Hanna kit and is my favorite kit that uses color. The Results are repeatable, and very easy to differentiate from one to the other level. The price is high at roughly 50 U.S. dollars, but you get over 150 tests per kit, which works out cheaper than a hanna. Just my 2 cents