TEST METER FOR TESTING NITRATES
Back in October of 2017 I posed about a DIY Test meter …The second post in Jan 2018 expanded the work to look at using the Hanna HI-736 PHOSPHOROUS Checker as the measuring instrument. As I mentioned at the end of the Jan post I was exploring the use of other Hanna Checkers mostly because I wanted to expand the measurement range. The HI-736 was good for low range Nitrate < 3ppm, but I wanted something that would measure up to 20 + ppm.
Here are the links to the previous posts:
Oct 15 2017 https://www.reef2reef.com/threads/diy-nitrate-test-meter.330892/#post-4114495
Jan 10 2018 https://www.reef2reef.com/threads/using-hanna-phosphorous-checker-hi-736-to-test-for-low-levels-of-no3.350062/#post-4815606
After looking at several I settled on the HI-764 ULR Nitrite Checker, using the Red Sea Nitrate Pro Test Reagents. It gave me an expanded range as well as very good precision. (See Data Below)
I use almost exactly the same test development protocol that I described in the October 15 2017 post (see link above). As well as the same testing protocol described in the video posted on Jan 10. The difference in the test development protocol was the concentrations of the calibration standards, and as mentioned in the Jan 10 post I used a standard salt solution to create the calibration standards. My calibration standards were 1ppm, 2ppm, 4ppm, 7ppm, 8ppm, 20ppm. All of there were prepared in salt water (reagent grade sodium Chloride)
I won’t bother you with the fine details of the test development. If you are interested PM me and I would be happy to answer your questions.
Below is the outcome of the work.
FIG 1 Are the regression results from measurements made on each of the calibration levels. Each level is the result of 6 independent measurements.
The regression model was generated using the Excel Data Analysis as well as MyCurveFit program. The Goodness of the Regression is solid (Data Below)
GOODNESS OF FIT DATA
P = 2.169 X 10-7
SE = .433
TEST PRECISION (Same sample tested on 5 different days 4 times each trial)
The test precision is quite good (ppm)
In order to check the accuracy of the results for the last 9 months I have compared the results to the Red Sea Pro test kit as well as the NYOS test kit. I took the measured results and checked them vs. the color range that the sample tested in both the Red Sea and NYOS test kits. A sample of the data can be seen below. If you are interested in the total data set I can provide it to you.
As you can see the meter test results very consistently fall within the range of both the Red Sea and NYOS Test kits.
I have completed my data collection and now only use the test meter data in measuring my nitrate levels. It is interesting to note that I can monitor the impact of my carbon dosing on the nitrate level. You can see this looking at the above data from dates 10/15/18 to 12/10/18. During this period I increasing the dosing to bring the nitrate levels down. The first increase was on 10/16/16 and the second one was on 11/5/18. It might be an interesting question to explore if it might be possible to quantify the drop in nitrate to a specific dosing amount??
The nitrate test development work is continuing. The need to look at levels below 1 ppm and above 20 ppm may have some value so I will continue the efforts towards that.
I am currently working, using a similar procedure on developing a Iodine test method. I am about 2/3 complete and am currently gathering data on the test precision and accuracy. It uses the HI- 707 Nitrite LR as the meter and the Red Sea Iodine Test Reagents. It is a bit trickier because the reaction is time and temperature dependent so that adds some complexity to the procedure but thus far I have some encouraging results. Hope to post the results in the not to distant future.
As you can observe from some of the posts on this Thread @taricha and @Dan_P have made important contributions to this effort. I would like to thank them for their support and efforts towards the goal of having more effective testing methods.
Well that pretty much wraps it up…Questions and comments welcomed.