I have used Hanna low nitrate checker some months and I´m rather pleased with it if you have readings below 5 ppm. However - when you need to dilute - you run into problems. You can´t dilute with RO water because the checker is adjusted to high chloride content and if you use newly mixed SW - you still get problem if it contain anything that will show up as nitrate in the test - and at least Red Sea pro (the red bucket) affect the readings. Even if you use pure NaCl in the water you use for dilution - it affect the readings, Let us say that the dilute water show up with 0.3 ppm NO3 - it will affect your final result with 3 ppm.
In order to avoid this problem - I do two tests. I use a volumetric flask of 100 ml and put in 3.5 g pure NaCl (table salt) - after that I fill the flask with RO water to the 100 ml mark. Mix well and suck out 10 ml of the mixed water with a syringer. After this I fill up the flask to the 100 ml mark again with 10 ml water from my aquarium. Mix well and put it away for a while.
From the syringer with 10 ml 35 promille water I take 7 ml and start the normal procedure for determine NO3 in a sample (the Hanna low nitrate procedure) The result I get from this pure water will be written down - last time it was 0.38 ppm.
Now I take the volumetric flask with my 10 times diluted sample - take 7 ml and start a new standard analyze of the nitrate in the diluted sample. Last time it show 3.5 ppm NO3.
Now the math starts - I diluted my tank sample 10 times with a saltwater that scontain 0.38 ppm NO3. It was 9 parts containing 0.38 ppm and 1 part containing x ppm Nitrate. The whole sample show 3.5 ppm - it means that I should take away 0.9*0.38 ppm from 3.5 ppm - giving me 3.15 ppm as result. But it was 10 times diluted - my tank contain 31.5 ppm NO3.
This method take some time but - it is the only method that have been working for me. First take a test of the water used to dilute with. Dilute 10 times - 9 dilution water 1 sample water. Take a new sample - read. Subtract 9/10 of the first result from the second result. Multiply with 10 - and you have X
Sincerely Lasse
In order to avoid this problem - I do two tests. I use a volumetric flask of 100 ml and put in 3.5 g pure NaCl (table salt) - after that I fill the flask with RO water to the 100 ml mark. Mix well and suck out 10 ml of the mixed water with a syringer. After this I fill up the flask to the 100 ml mark again with 10 ml water from my aquarium. Mix well and put it away for a while.
From the syringer with 10 ml 35 promille water I take 7 ml and start the normal procedure for determine NO3 in a sample (the Hanna low nitrate procedure) The result I get from this pure water will be written down - last time it was 0.38 ppm.
Now I take the volumetric flask with my 10 times diluted sample - take 7 ml and start a new standard analyze of the nitrate in the diluted sample. Last time it show 3.5 ppm NO3.
Now the math starts - I diluted my tank sample 10 times with a saltwater that scontain 0.38 ppm NO3. It was 9 parts containing 0.38 ppm and 1 part containing x ppm Nitrate. The whole sample show 3.5 ppm - it means that I should take away 0.9*0.38 ppm from 3.5 ppm - giving me 3.15 ppm as result. But it was 10 times diluted - my tank contain 31.5 ppm NO3.
This method take some time but - it is the only method that have been working for me. First take a test of the water used to dilute with. Dilute 10 times - 9 dilution water 1 sample water. Take a new sample - read. Subtract 9/10 of the first result from the second result. Multiply with 10 - and you have X
Sincerely Lasse