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For what it is worth, I made a table of results using these tests, each one being performed immediately after the prior one:
RUN #1: Tested sample with "Regular" Precision
RUN #2: Tested sample with "Regular Precision
RUN #3: Tested sample with "High Precision"
RUN #4: Tested sample with "High Precision"
Next Row in Table shows Salfert test results on same sample (and *ICP result from 5 weeks ago for Na, just out of curiosity)
RUN # 5: Multi-Reference Solution (High Precision)
RUN #6: Multi-Reference Solution (High Precision)
Multi-Reference Solution's Reference numbers.
PARAMETER CA MG K Na NO3 1st Run (Reg) 454 1370 435 10,754 6 2nd Run (Reg) 454 1367 435 10,754 3 3d Run (High Precision)
441
1311
429
10,605
124th Run (High Precision)
445
1317
430
10,621
5SALIFERT/ICP* 440 1335 390 10,269* 1 MULTI-REF
(TEST #1)
411
1317
382
10,610
11MULTI-REF
(TEST #2)
427
1384
388
10,729
4MULTI-REF
(REFERENCE VALUES)
420
1300
390
10,700
11
What numbers are you expecting to see from the IOND?
Are you expecting a near 1:1 match from a hobby grade kit?
It won't happen. Different technology, different measurement process.
Are you expecting a near 1:1 match from an ICP test?
It won't happen. Different technology, different measurement process and other variables.
Do you know if the ICP lab is following the necessary maintenance schedules on their machine for optimal performance? What is the tolerance level of their ICP machine? Do you know if the test you received is within said tolerance?
Did your impressions take into account the tolerances of multi-reference fluid and IOND device itself?
Based on the IOND numbers you shared, those are spot on and very consistent.
Because of the different technology behind the IOND, ICP and conventional kits, comparing them with each other as a reference is not ideal. It's like comparing apples to oranges to pears. We've seen this kind of comparisons done with other auto testing machines too and there's always the question of "why the difference?". The answer is always the same. Different technology and different measurement process. As @CEReefer said, it's going to take some getting used to the new way of looking at the data.
At the end of the day, in reef tanks, it's the consistency within a desired range that matters most. Take nitrate for example. Some will tell you to keep it between 2-5, others 5-15. Each person will have their own set of desired values they aim for. Unfortunately, some get fixated on the numbers and feel that "something is wrong" when the result is not the number they expect to see. With the IOND, some may even feel something is "wrong" when the past number is not 1:1 with the new IOND result. It is especially important to know and take the tolerances of the device into account when formulating initial impressions. Unfortunately, the tolerances of measuring devices are often overlooked.
In order to really understand the numbers behind each IOND result, it's important to also understand how multi-ion sensors detect these 5 parameters in your sample of water. I'm going to try to put is in as short words as possible...
In our tanks, we have a sea (no pun intended) of ions. Within that pool you have Sodium, Magnesium, Calcium, Potassium and Nitrate. The more ions present in the water, the "easier" it is to detect. Take Sodium for example. We measure this in the 10,000. Now let's compare that to Mg which is measured in 1,000. Compare that to Ca and K which is measured in 100s. Lastly, NO3 which is measured in 1s and 10s. As we make our way to measuring NO3, we can say that there are significantly less NO3 ions in the water than Ca, K, Mg and Na. For an MUI sensor, measuring NO3 ions in a sample of water is like finding a hair in a haystack. It can be done, but it requires a higher degree of sensitivity. Hence the NO3 tolerance of +/- 2ppm (HP mode) and +/- 3ppm (Standard mode).
You can see an NO3 value of 11, then do another test and get 8 or 14.
Does this mean the IOND is wrong? No, not necessarily. It could mean two things. The device is performing within the specified tolerances or NO3 changed from 11 to 14 in a day (it is possible). In the end, whether the "real" NO3 is 8, 11, or 14...will the coral's health decline because of it? Unlikely.
It's the consistency within the desired range considering tolerances that matter most.
Of course, if one really wanted to get their IOND numbers to match the parameter values of the Multi-Ref solution 1:1 or another more trusted source, they have the option to do that with the offset feature.