Its not easy. I had to work out a methode there Hannah's HI-774 accuracy of plus minus 0.02 does not play a major role. I do like this. I prepare 3 sample vial. 1 vial is the zero - the other two is my samples. Fill up with 10 ml test water en each vial. Take the zero, clean the outside thoroughly with a towel. Put it in the Checker. press two time till C2 comes up. Take sample 1 and put in the checker instead for the zero. Press once very short - the checker will analyse the first sample (without reagents) - should show up 0.00 - if not clean again till it show up 0.00 (using the same method - the zero - press twice - C2 show up and after that - put in sample 1 and a short press. When sample 1 shows the same (0.00) as the zero - I do the same with the vial containing sample 2. Now I put the zero away for a while and put in reagens in sample 1 and 2. Turn upside down in two minutes. Clean and put aside after 2 minutes. Put the zero sample in the checker, press two - till C2 shows - now press a long press till 3 minutes start to count down. After 3 minutes the checker will read the zero sample and it will show 0.00. With the zero sample in the checker press till yo se C2 again. Switch to sample 1 and a short press - the checker read the sample 1 - and you have the first result. Write it down. Do the same with sample two (but no 3 minutes) - put zero sample into the checker - press till C2 and switch to sample 2 - shor press and it read sample 2. Write down the figure. Put in zero sample - press till C2, switch to sample 1 - press short and you will get your second result. I have done this eleven times with each sample. After that I take away 1 lowest reading and 1 highest reading of each sample - leaving 9 samples to take an average of. Put together the average of both sample 1 and 2 and a new reading - this is my result!! It take around 10 minutes to analyse both samples this way with 11 individual readings against the zero sample. The question is if the colour will change during 10 minutes after the three minutes of developing. I have done trend lines off all my tests and - yes - it can change a little - but in both directions. The tendency is however much lower than the accuracy - so I think that I get a better precision with this method. Yes - when you do 11 test of the same sample after each other - you will note the plus minus 0.02 ppm very well. Som examples. It is ppm PO
4 that have been measured
My goal was to do a complete test round every 4 hours. I did take automatic samples 00:00 and 4:00 but the result change too much during 4 and 8 hours prior the analyse - I had to take away these results. Below you will see the result between 20-03-02 and 20-03-05.
I have done nearly 75 test but I´m not satisfied with my methodology. I have seen that I normally have my highest reading around 12:00 and the lowest around 20:00. I will run another serie of test during maybe 5 - 7 days with sample times 08:00 and 20:00 on workdays and 08:00, 12:00 and 20:00 other days. I have done test the last 8 days but it is first the last 3 days I satisfied with part of the methodology. I have logged the result together with my pH. The result indicates lower readings in the end of the light period and at the top of the pH. For some people it maybe indicate a chemical reaction (bound and dissolving of calcium phosphate) and for some it maybe indicate an uptake by photosynthesis. Maybe are the truth something between. However - it can´t be seen in this diagramme below - test I have done at 12:00 looks to have the highest concentration of PO
4 - but the pH is not lowest at that time.
I will be away from home for 10 days now so I have to wait with my test till the end of march and hope to come back with a better investigation. It looks like I have a general rise in PO4 too, therefor I will run a lower amount of GFO during my vacation.
Sincerely Lasse