[aquabillpers]

Phosphate Test Kit Comparison

April, 2007
​

Four phosphate test kits were tested: those distributed by American Pharmaceuticals (API), Red Sea, Nutrafin/Hagen, and Seachem. The primary emphasis of the tests was on the accuracy of the results, but other characteristics of the test kits that affected their utility were noted.

Three of the kits were purchased on line from Drs. Foster and Smith; the fourth, from a local pet shop. All were acquired within the past month.

Each test kit cost about ten dollars.

Each of the kits tested the sample by adding two or three reagents to a test sample and
comparing the result to a color chart.

Summary

The Seachem kit was the most accurate of the four. All three of its tests agreed with the computed Fertilator results. The Seachem kit was also the easiest to use and had a shorter final stage "wait" time, of about 25 seconds. The other kits had wait times of two to three minutes.

The Red Sea and Hagen/Nutrafin kits gave usable approximations at levels of 1.0 PPM or less.

The API kit produced unusable results.

Color Charts

The API chart contained six separate color bars corresponding to 0.0, 0.5, 1.0. 2.0, 5.0, and 10.0 parts per million (PPM). The Red Sea chart's color bars were labeled 0.0, 0.1, 0.2, 0.5,
1.0, and 2.0. The Nutrafin/Hagen chart covered 0.0, 0.25, 0.5, 1.0, 2.5, and 5.0.

The Seachem color comparison chart was a bit different. Instead of consisting of six discrete blocks of color, it was a 3.5 inch strip of continuous color, with labeled gradations of 0.0, 0.05, 0.1, 0.2, 0.5, 1.0, 1.5. 2.0. 2.5. and 3.0. This was easier to use than the discrete color block charts.

Other Comments

As indicated below, the API test of lower concentrations produced poor results. An email was sent to advise them of the problem. They responded to it about three weeks later, two days after this comparison was posted, with a request for lot numbers.

The Nutrafin/Hagen kit used a test vial with a rounded bottom and a heavy paper stand to hold it. The cap of the test vial was not water tight. The other kits employed test vials with flat bottoms and water-tight caps. If the heavy paper stand should become unusable it would be more difficult to use this kit.

Test Results

Caveats: Since the evaluation of the results of a test involves comparing the color of a solution in a tube to a test chart, the eyesight of the tester could affect the results. Also, even the best of test kit manufacturers can make a mistake and produce a substandard kit. And, test kits have finite lives. While the four used in this test were recent purchases, none had a "date packed" or a "use by" date.

Test 1. Distilled water:

Red Sea - 0.0 to 0.1 PPM

Seachem - 0.05 to 0.1

Nutrafin/Hagen - 0.25

API - 0.5 to 1.0 (The actual color was a bluish green that didn't match anything on
the chart very well.)

Test 2. Water from a 150 foot deep residential well in southeastern PA, USA:

Red Sea - 0.0 to 0.1 PPM

Seachem - 0.1 to 0.2

Nutrafin/Hagen - 0.25 to 0.50

API - 0.5 to 1.0 (The actual color was a bluish green that didn't match anything on
the chart very well.)

Test 3. Two drops of Fleet Enema in 2 gallons of distilled water:

Fertilator (with correction factor) - 2.11 PPM

Red Sea - 0.7 to 0.9

API - 2.5 plus

Seachem - 2.0

Nutrafin/Hagen - 0.8 - 0.9

Test 4. One drop of Fleet Enema in 2 gallons of distilled water:

Fertilator - 1.06 PPM

Red Sea - 0.6 to 0.7

API - 0.5 to 1.0

Seachem - 1.0

Nutrafin/Hagen - 0.8 - 0.9

Test 5. One-half drop of Fleet Enema in 2 gallons of distilled water:

Fertilator - 0.53 PPM

Red Sea - .03 to .04

API - 0.5 to 1.0

Seachem - 0.5

Nutrafin/Hagen - 0.25 to 0.5

 

[aquabillpers]

Interesting and a lot of work. Thank you for sharing this. Sounds like Seachem is fairly reasonable. I though Saechem kits had a sell or use by date though? Maybe it was a made on date. The reagents definitely had something last time I looked at one.

Dennis,

The two reagent bottles in the kit that I tested have lot numbers but no dates.

Bill

I use Seachem's Nitrite/Nitrate and Phosphate test kits and I really like them for their ease of use. I'm glad that you found the phosphate test kit to be fairly accurate.

I have a question, how in the world did you produce a 1/2 drop test sample with these test kits?

Well, Left,

Using a dissecting microscope and a small scalpel, I . . .

Actually, I mixed 2 drops of Fleet with 12 mm of distilled water. Then I removed 3 mm of that solution to obtain the half-drop equivalent that I mixed with the distilled water for the test.

Bill

Great job, but something was wrong with the Hagen kit. I use tons of these and they never fail. When zero ppm, DI or RO water is used the color is white-greenish indicating zero. The test chart is a scale of blue intensities. Clearly green water indicates zero. This can surely be confusing because the test chart shows transparency for zero level, not green.

Also, using Fleet Enema is not the greatest idea. This medication comes in more then one concentration and may be made of more then one ingredient.

Edward,

We might be talking about different test kits. The one I tested was in a box labelled "Nutrafin" but the color scale was labeled "Hagen." The color scale starts at a slightly off-white (for no color) for 0.0 PPM and rises in stages to a violet blue for 5.0 PPM. In the tests I saw nothing close to green.

There are at least two kinds of Fleet Enema. According to the distributers, the phosphate one contains monobasic sodium phosphate (19g) and dibasic sodium phosphate (7g). I would think that the manufacturer would be quite careful to maintain those levels. The (adjusted) phosphate levels computed by the Fertilator were in agreement with that determined by the Seachem kit.

Thanks, all, for your comments.

Bill

 

[aquabillpers]

I have edited the comparison to reflect the fact that today I received a reply to my email to API of April 9, in which I told them of the poor results of the test of their phosphate test kit. API requested the lot numbers of the reagents and I sent that to them.

This forum has a such a broad readership!

Bill