I am nearing the end of my algae battle so I am doing an overnight test. I am a bit concerned about how to make the test accurate each time. Please understand that I have been using the FAS-DPD titration of testing for 5 years so I am comfortable with the process, but......
In a past test kit, I received a measurement spoon for the DPD powder that was nearly twice the size of the small blue spoon. I haven't used that one in a long time, but I did use it during my test accuracy trial this morning. I have always read on this forum and others recommending this test that the amount of powder does not make a difference and that it will titrate out the same nor does it matter if all the powder dissolves. This is not true according to my tests this morning.
All tests using a water sample removed from the pool at 1 time and used to rinse the test vial between tests.
Test #1
used level blue scoop of powder (well as level as I could make it with the larger powder granules) - not all granules dissolved
FC = 14
Test #2
used level blue scoop of powder (well as level as I could make it with the larger powder granules) - not all granules dissolved
FC = 15
Test #3
used blue scoop with more of a heaping scoop of powder - not all granules dissolved
FC = 16
Test #3
used larger white scoop of powder nearly level - not all granules dissolved
FC = 17.5
So from this, I determined that the amount of powder dissolved does effect the result of the test. I also learned that even when trying to make the scoop of powder the same, I may not get the same result. When trying to determine if my overnight test revealed that I am done "shocking", I look for a less than 1 FC drop. Now I have to determine which test to use as accurate. Last night I got an FC of 15.5. If I use the result of test #1 - I need to keep shocking. If I use #2, I am done.
How do you know if you go the same exact amount of powder in each test when comparing? And how do you know if the same exact amount of powder dissolved in each test?
In a past test kit, I received a measurement spoon for the DPD powder that was nearly twice the size of the small blue spoon. I haven't used that one in a long time, but I did use it during my test accuracy trial this morning. I have always read on this forum and others recommending this test that the amount of powder does not make a difference and that it will titrate out the same nor does it matter if all the powder dissolves. This is not true according to my tests this morning.
All tests using a water sample removed from the pool at 1 time and used to rinse the test vial between tests.
Test #1
used level blue scoop of powder (well as level as I could make it with the larger powder granules) - not all granules dissolved
FC = 14
Test #2
used level blue scoop of powder (well as level as I could make it with the larger powder granules) - not all granules dissolved
FC = 15
Test #3
used blue scoop with more of a heaping scoop of powder - not all granules dissolved
FC = 16
Test #3
used larger white scoop of powder nearly level - not all granules dissolved
FC = 17.5
So from this, I determined that the amount of powder dissolved does effect the result of the test. I also learned that even when trying to make the scoop of powder the same, I may not get the same result. When trying to determine if my overnight test revealed that I am done "shocking", I look for a less than 1 FC drop. Now I have to determine which test to use as accurate. Last night I got an FC of 15.5. If I use the result of test #1 - I need to keep shocking. If I use #2, I am done.
How do you know if you go the same exact amount of powder in each test when comparing? And how do you know if the same exact amount of powder dissolved in each test?