Got my salinity up with a water change, but only temporarily?

[BeanAnimal]

Your reference for this assertion?

Thousands (tens of thousands?) of aquarists rely on refractometers and maintain healthy systems, I don't think there is any argument there.

I own a small pile of refractometers and have spent considerable time (sadly) comparing them over a wide range of salt concentrations. They are not all linear with respect to each other. The error or non linearity may be in the prism/lens assembly or due to poorly printed or etched scales, who knows.

Without mentioning names or models, it is very clear that some instruments are of much higher quality than others and many of them are the same low quality product re-branded under many names and colors.

Some of the units do not show a crisp lines when being read and are prone to reading error, other units may show a crisp line but may vary by +/- 2PPT depending on the way the plastic cover is situated during a reading.

Lastly, Our own Randy Holmes Farley explains some of the reading errors here:
http://reefkeeping.com/issues/2006-12/rhf/index.php

Please take note of the "Slope Miscalibration" section. If a given refractometer has error in this realm and it is not calibrated AT the exact target concentration, then it will read in error at the target concentration.

There is another long thread (and article if I remember) where Randy and others compared several well known refractometers and listed one or two that do not calibrate properly and therefore read in error.

And by the way, unless the LFS are using salinity of 1.009 it will have no affect on parasites. Many LFS keep reduced salinity to save money on salt. And of course, if you buy a fish that is being kept in 1.019 SG and want to put it into your tank at 1.025/6 you have some adjustment to do.

There is no argument there at all. I simply pointed out the reason given by most LFSs I have talked to. I would agree that it saves salt, but does nothing (at the levels they keep) to prevent parasites or infection.

 

[JPMagyar]

But for our purposes match the concentration scale fairly well, as our temperatures are within a rather narrow range.

In reality neither are that important for MOST of the living creatures that we keep. Salinity and temperature can vary over a fairly wide range and the livestock will easily thrive. . .

I would disagree with this analysis because a variation of 5 degrees celcius changes SG by 0.002 and then if one adds calibration error and human reading error on top of that I believe it is not uncommon to be off by 10% in the ionic solution. My own experience showed that I ran my tank for years at 31 to 32 ppt because of a combination in errors which to me is proof positive that it can and most likely does happen to many aquarists.

Without a doubt ocean creatures come from and can survive in a seemingly wide array of conditions but here again I would argue with the word "thrive". My system, I believe, has finally reached a "zenith" and I believe changing from 31 ppt to 35 ppt made a big difference as my pH, alkalinity, calcium, and magnesium all came into line once I got my salinity right.

But then that's the beauty of RC, lots of GREAT info and opinions to help us all get better!

Joe

 

[snorvich]

Without a doubt ocean creatures come from and can survive in a seemingly wide array of conditions but here again I would argue with the word "thrive". My system, I believe, has finally reached a "zenith" and I believe changing from 31 ppt to 35 ppt made a big difference as my pH, alkalinity, calcium, and magnesium all came into line once I got my salinity right.

That has also been my experience. One of the Elos tests,
the one for Mg, has a component that has been a very accurate inference of SG. When SG is correct, most everything else seems to be proper or at least controllable.

 

[BeanAnimal]

I would disagree with this analysis because a variation of 5 degrees celcius changes SG by 0.002

5 Degrees Celsius is 9 Degrees Fahrenheit so even in a tank that has fairly substantial temperature swings, there will not have a 5 Celsius differential between readings. In all but extreme cases the differential will be 1C or less, giving an error of SG 0.0004 or less.

You are over thinking the error and the impact on the system while at the same time assuming that the refractometer has no error in function or when being read by a human.

Steven Pro took the time to measure the results from many random hydrometers several years ago and publish the results:
http://www.wetwebmedia.com/ca/volume_3/cav3i4/hydrometers/Impressions.htm

Again, the hydrometers sold to this hobby are (in most case) perfectly acceptable instruments when compared to the refractometers sold to this hobby. Either instrument will provide perfectly acceptable results if properly maintained.

Without a doubt ocean creatures come from and can survive in a seemingly wide array of conditions but here again I would argue with the word "thrive". My system, I believe, has finally reached a "zenith" and I believe changing from 31 ppt to 35 ppt made a big difference as my pH, alkalinity, calcium, and magnesium all came into line once I got my salinity right.

Your point was that Temperature and Salinity are two of the (if not most) important parameters with regard to reef aquarium husbandry. There are certainly countless systems that do in fact THRIVE with salinity and temperature parameters that fall over a wide range of values.

Again, our livestock comes from all over the globe, where temperature and salinity values differ from habitat to habitat. There is no single target point that is "best" and most living organisms are capable of easily adapting

 

[JPMagyar]

5 Degrees Celsius is 9 Degrees Fahrenheit so even in a tank that has fairly substantial temperature swings, there will not have a 5 Celsius differential between readings. In all but extreme cases the differential will be 1C or less, giving an error of SG 0.0004 or less.

You are over thinking the error and the impact on the system while at the same time assuming that the refractometer has no error in function or when being read by a human.

Actually I was thinking more along the lines of errors introduced by failing to calibrate refractometers at 20 degrees C or 68 degrees F ambient room temperature. Here's a quote from Sybon the manufacturer of the refractometer used in Steven Pro's article:

(Note: For precision, it is very important to
do the recalibration steps at an ambient temperature of 20 Celsius degree!)

This is because if you recalibrate at a room temperature of 78 degrees you are setting your zero point off by an amount greater than 0.001 which in turn can put your salinity off by 2 ppt which means your calcium level is off by 25 ppm and that's with only one error.


I will admit I am fascinated by the results Steven got in the article although I would find myself better persuaded if he had been able to use models that had been in use for a year or more. I also agree that I am taking this to a level of discussion that is both unnecessary and uninteresting for most folks, but hey call me OCD :beer:

And your excellent points have caused me to refine my primary comment which I do still believe: I feel salinity is the single most important factor in maintaining a healthy SPS dominated reef for the large majority of reefs seen here on RC. (How's that for hedging my bets :lol2: )




Joe

 

[muppet]

Well guys, after carefully following this thread for the past couple of days, and I've decided to give up the hobby entirely as I'm clearly unqualified to own fish, lacking any advanced degrees in organic chemistry or physics. Thanks for the input!

 

[BeanAnimal]

I thnk what most folks can walk away with is that all of the devices that are available to us have roughly the same magnitude of error and must be calibrated by one means or another to minimize that error. This includes the Pinpoint salinity meter, hydrometers and refractometers.

Like many things, sometimes it is not so much the actual measured level that is important, but the ability to take measurements that show a consistant tested level in the healthy system

Wirth regard to calcium levels, they really are not that important as long as they are somewhat in balance with the alkalinity levels, and even to that end, the bandwidth in the "balance" area is fairly wide. Randy Farley has pubished several well authored articles on this subject.

FWIW as part of the experiment, Steve also included used hydrometers with the same results

Lastly, if you spend a bit of time looking, you will find many beautfiful SPS systems that have a much lower (or higher) salinity than you expect. There are many variables that affect system health but if you are looking for a silver bullet, in most cases efficient nutrient export is they key to success or failure.

FWIW I use a refractometer, as I donated one of my hydrometers to Steve Pro and srtepped on the other when cleaning the fish room The reason I have so many is because of the disagreement between readings from model to model.

 

[fasteddie68]

This is a helpful link that graphically shows the relationship between temperature, salinity and specific gravity: http://www.msc.ucla.edu/oceanglobe/pdf/temp_densal_chart.pdf

One additional point. If you extract water from a tank at 78 F and place a couple drops onto a refractometer that's at a room temperature of 68 F the water will quickly equalize to the temperature of the larger mass - the refractometer - and the water will no longer be 78F but 68F. As a result you will get a reading for 68 F salt water which will be different than a reading for 78 F salt water all other things being equal. Now take a look at the chart and look at the difference 5.5 degrees C (10 F) has on the sample. It's a measurable difference, not giagantic, but certainly observable.

Getting back to the original question of this post, a temperature differential between the water or the test instrument in between readings over a couple days may indeed account for the "missing" salt.