Refractometer Calibration

PSam · #1 12/11/2007, 08:08 PM

Read RHF's article and read a bunch of searched threads. I'm down to 2 options and was wondering which you all do or think is best...

Calibrate to 35ppt with 53 ms and always target 35ppt or,

zero the refractometer with the 'ultrapure' water supplied with the instrument, then drop some pinpoint 53ms on it and use the reading from the 53 ms solution as a target (it turns out about 37 or 38).

I think it's easier for me to remember the 35ppt instead of remembering some target that I wouldn't keep my tank at on purpose.

bertoni · #2 12/11/2007, 08:14 PM

Either way will work, but calibrating with pure water might be easier for a fast check of the status of the refractometer.

Billybeau1 · #3 12/12/2007, 02:33 AM

From my experience, if you use the 53 mS fluid and adjust to 35ppt or 1.0264, you are good to go. I never liked using even ultra pure water on a refractometer even though the manufacturer recommends it.

Hasn't worked for me.

Randy Holmes-Farley · #4 12/12/2007, 08:23 AM

If you have a sample that is 35 ppt equivalent for sure somehow, then I'd use that, at least once to check to see if the different methods give the same results or not.

capn_hylinur · #5 12/12/2007, 07:14 PM

There seems to be alot of threads lately on calibrating refractometers.
Is it really necessary to get bent out of shape about salinity accuracy given a comfortable acceptable range of .024-.026? Some reefers use higher levels--I believe JB stated he prefers to run his at .027?
You guys know me by now that I believe in chemical accuracy but it just seems lately like everyone is concerned about refractometers being dead on or even wearing out.

Compared to test kits aren't refractometers fairly stable in accuracy?

I really don't understand what parts can wear out in these--if you take care of them, rinse the saline off etc.

bertoni · #6 12/12/2007, 10:53 PM

I use a conductivity meter, and I target 53 mS. I think it's worth calibrating a refractometer from time to time. They do seem to slip out of adjustment.

scaryperson27 · #7 12/12/2007, 11:49 PM

You don't want to calibrate the refractometer to read 0 perfectly because you aren't testing in that range. You want the refractometer to be most accurate within the range that you are testing, 35ppt/1.0264.

If you try calibrating it with fresh water, the refractometer will most likely be .001 off on the specific gravity reading (from what I've heard).

It all depends on the amount of accuracy you prefer. You bought into one of the more expensive forms of reading specific gravity so i would assume you would want it to be most accurate.

sjm817 · #8 12/12/2007, 11:55 PM

Quote:

Originally posted by capn_hylinur
There seems to be alot of threads lately on calibrating refractometers.
Is it really necessary to get bent out of shape about salinity accuracy given a comfortable acceptable range of .024-.026?

Yes. Here is my example: I mixed my Reef Crystals Salt mix @ what I thought was 1.026, but was actually 1.023 because of a refractometer calibration issue. My ca was 360. I always had to boost it up. Once I had the refractometer set correctly, my salt mixed up with a ca of 420. I'm sure my alk, mg, other elements were lower than they should be as well.

Billybeau1 · #9 12/13/2007, 02:16 AM

I here you sjm. You are right on, from my testing.

Randy, since you've been gone for awhile (well deserved I might add.)

I have found that calibrating a refractometer with the Pinpoint 53 mS calibration solution seems to be the most accurate calibration to date for even the $50 refracts.

I have tested this with a lab grade floating hydrometer and am convinced the results are real.

My refract is off .003 when testing with ro/di as opposed to the Pinpoint 53 mS solution. I believe this has something to do with the refractive index you wrote about some time back.

I sure wouldn't mind you testing this theory yourself, if you have time.

BTW, some refracts actually tested the same with ro/di and this calibration fluid. I think jd had one. Maybe check with him.

PSam · #10 12/13/2007, 12:14 PM

Quote:

Originally posted by capn_hylinur
Is it really necessary to get bent out of shape about salinity accuracy given a comfortable acceptable range of .024-.026? Some reefers use higher levels--I believe JB stated he prefers to run his at .027?

I don't care so much about if it's 1.027 or 1.025, etc, as much as I care about my make up water being exactly the same as my tank. I need the refract to be calibrated correctly so I can achieve this. Not to mention, I am using products to run a 'low nutrient' system, and NSW levels are recommended, and stability is important.

capn_hylinur · #11 12/13/2007, 12:29 PM

thanks for putting this into perspective guys--I am a believer now

mcneilwh · #12 12/13/2007, 06:47 PM

I always like to keep secondary standards. Like one of those cheap plastic hydrometers. Once you get your everything calibrated with your refractometer check it with the plastic one, then clean it and put it away, but note the difference. In the future if you suspect a problem them use the plastic one as a double check, the difference should be the same.

I do the same with my pH probe on my Neptune controller. I double check with one of the cheap colormetric pH kits. When I note a difference I pull out the calibration standards.

scaryperson27 · #13 12/14/2007, 12:41 AM

Quote:

Originally posted by PSam
I don't care so much about if it's 1.027 or 1.025, etc, as much as I care about my make up water being exactly the same as my tank. I need the refract to be calibrated correctly so I can achieve this. Not to mention, I am using products to run a 'low nutrient' system, and NSW levels are recommended, and stability is important.

If you're measuring the NSW with the same refractometer as your tank then why would it get a different result?

mcneilwh · #14 12/14/2007, 09:18 AM

All calibration tools drift over time. This is just a way to check your measurement tools.

I know of at least two fellow reefers now that think that their refractometer is perfect and is never wrong. Then when we exchange frags it looks like I am mixing oil and water from the salinity difference during acclimation.

If all you need is a comparison of specific gravity then you don't need to calibrate anything. Just measure your target, and then adjust your sample to match the target while using the same measurement tool. But the does not help track the drift of your tank salinity over time due to evaporation or addition of additives.

capn_hylinur · #15 12/14/2007, 01:14 PM

Quote:

Originally posted by mcneilwh
. But the does not help track the drift of your tank salinity over time due to evaporation or addition of additives.

sorry, this might be a touch of hijacking but that last sentence might be an anwer to my strange raise in salinity levels

I keep the salinity at .026, pH at 8.09, alk at 9.8dKH, ca at 400 and mag at 1290. I have been using the b-ionic two part for a little over 4 months. Lately(because I started measuring salinity level again in the tank) I have notice a rise from .026 to .027 and sometimes .028.
I do 20 gals water change using r/0 every two weeks and top ups average 5 gal every two days with r/0 water.
About every two weeks or so I have to make a slight adjustment in ca, alk, and mag. I use kent dkh, calcium and tech-m. But very miminally.
The salt water is prepared in a 30 gal plastic pail, heated and agitated with a power head two days prior--and the salt is tested at .026 through out the pail. (I am using instant ocean)
I test the main tank before, just after in the sump before circulation resumes, and about 1-3 hrs after--it is always .026

any thoughts on the rise in salinity over a two week period?

Thanks
Scott----and I am sorry to the original poster but this seems related

Randy Holmes-Farley · #16 12/14/2007, 02:32 PM

Salinity will rise with the use of two part systems due to the residual ions left in the water:

How to Select a Calcium and Alkalinity Supplementation Scheme
http://www.advancedaquarist.com/issues/feb2003/chem.htm

from it:

The rise in salinity of these products over time can be very roughly calculated, though there are several reasons why this calculation is only an estimate. For every 1000 meq of alkalinity added in this fashion (and the matching amount of calcium) these products will deliver on the order of 60 grams of other ions to the tank. In a tank with a low calcification demand (defined later to be 18.3 thousand meq of alkalinity per year in a 100 gallon tank (50 meq/day)) this effect will raise the salinity by 3 ppt per year (compared to a normal salinity of S ~35). In a high demand tank (defined later to be 219 thousand meq of alkalinity per year in a 100 gallon tank (600 meq/day)), the salinity will rise by 35 ppt in a year, or approximately doubling the salinity. Consequently, the salinity should be monitored closely in using these types of additives, especially in a tank with high calcification rates.