HELP! Perimeters are to high

[stevedola]

Again, all I am saying is that to test your batches of salt and be aware of what it mixes to. Here is a group of test done by experienced hobbyist and a lab. You can see the variance. It has happened in the past where batches of salt have large deviations from the companies stated values. I believe IO and tropic marin had a recall a few years ago for consistency issues.
Red Sea Coral Pro
Date performer SG Cal ALK MAG
8/19/2016 Triton lab 33.08ppt 441 NA 1436
8/19/2016 member 77F 35ppt 460 12.16 1440
10/12/2016 member 77F 35ppt 450 8.9 1350
10/12/2016 member 33.55ppt 440 9.3 1340
10/12/2016 member 77F 35ppt 440 11.84 1410
10/12/2016 member 34.6ppt 434 9.5 1363

 

[mr_tap_water]

Again, all I am saying is that to test your batches of salt and be aware of what it mixes to. Here is a group of test done by experienced hobbyist and a lab. You can see the variance. It has happened in the past where batches of salt have large deviations from the companies stated values. I believe IO and tropic marin had a recall a few years ago for consistency issues.
Red Sea Coral Pro
Date performer SG Cal ALK MAG
8/19/2016 Triton lab 33.08ppt 441 NA 1436
8/19/2016 member 77F 35ppt 460 12.16 1440
10/12/2016 member 77F 35ppt 450 8.9 1350
10/12/2016 member 33.55ppt 440 9.3 1340
10/12/2016 member 77F 35ppt 440 11.84 1410
10/12/2016 member 34.6ppt 434 9.5 1363

I totally agree with you,
In the sense that inconsistency with different batches and it is something to be aware off and not take for granted what it says on the side of the bucket I would also advise to mix it well when first buying so when you are doing your mixes you should get a more balanced reading.


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[mr_tap_water]

In some cases, RO/DI or distilled water will be just as good, but that isn't necessarily the case. I think that is why this is still such a debated topic. For some reefers, this method is accurate, but for others it isn't. It really depends on the refractometer: calibrating with freshwater assumes that the refractometer is consistent across the entire range of measurement. There's a vast difference in measuring the refractive index of freshwater and measuring the RI of saltwater.

Check out Randy Holmes-Farley's points on slope miscalibration. The long and short is that some refractometers may not be accurate over their entire range of measurement. That means by calibrating to 1.000SG you are ensuring that the reading is accurate at 1.000SG. However, as salinity goes up, small errors in accuracy become compounded, and get larger and larger:

In this hypothetical case, calibrating with freshwater produces inaccurate salinity readings. The refractometer will say your water is 1.026SG, when in reality it is closer to 1.024. Here is what happens when we correctly calibrate this hypothetical refractometer with calibration fluid:

Notice how the red and green lines are split at the bottom of the graph? What this means is that when you read freshwater with this hypothetical refractometer, it will actually read higher than 1.000SG. But that's okay. This refractometer is not consistent across its entire range. What we do know, however, is that the refractometer is exactly accurate at 1.026SG because we calibrated at that point with calibration fluid.

Calibrating with freshwater will still produce consistent results, and since consistency is really key with salinity, it likely won't hurt anything in your tank. However, it could produce inaccurate results. The only way freshwater calibration would produce accurate results at higher ranges is if your refractometer was consistent across the entire range of measurement. With hobby-grade refractometers, this is not a bet I'd be willing to take. There are some out there that will measure accurately at both ends of the scale, but I haven't had much luck finding one.

We spend hundreds to thousands of dollars on our reef setups. When calibration fluid is just $7 shipped, calibrating with freshwater to get "close enough" just doesn't make any sense to me. But, to each his own.

Interesting read and I take on board what you say,
To my defence though for the last eight years with the system I have i've always used RO and was advised by my local shop to to use RO even talking to some of the bigger chain stores in reefing also saying they use RO water to, and was no need to buy calibrating fluid as they said it was a waste of money, so being that it is debatable subject I took their word on it, and like I say this particular tank has been running now nine years with no problem ,but now will go out the way to get some calibrating fluid and test to see for myself if not just to settle my own peace of mind.
Again thank you for sharing your information.


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[chipmunkofdoom2]

Interesting read and I take on board what you say,
To my defence though for the last eight years with the system I have i've always used RO and was advised by my local shop to to use RO even talking to some of the bigger chain stores in reefing also saying they use RO water to, and was no need to buy calibrating fluid as they said it was a waste of money, so being that it is debatable subject I took their word on it, and like I say this particular tank has been running now nine years with no problem ,but now will go out the way to get some calibrating fluid and test to see for myself if not just to settle my own peace of mind.
Again thank you for sharing your information.


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No trouble at all. That wasn't meant to be a personal attack at all. It's just a complex issue because as hobbyists we don't discuss the details. We like to boil things down to "rules of thumb" and "it worked for me so it's likely fine." I was just hoping to introduce a bit more information into the discussion.

It's not necessarily wrong to calibrate with freshwater. It's just a bit more complicated than saying "freshwater works as a calibration fluid" or "freshwater doesn't work as a calibration fluid."