Calibrating refractometer and temperature compensation.

[Randy Holmes-Farley]

When you write:

" As it stands two Coralife hydrometers are getting a 1.027 and 1.028 while the refractometer is showing 1.022 with the calibration solution. "

Do you mean the calibration solution in the hydrometers? It may not be suitable for a hydrometer, even if it is perfect for calibrating a refractometer.

 

[flyfisher2]

No, I'm sorry for not being clearer. I compared two identical Coralife hydrometers, each respectively showing 1.027 and 1.028 to the refractometer which showed 1.022 when I used the calibration solution as opposed to distilled water.

I only used the calibration solution and distilled water with the refractometer.

 

[Randy Holmes-Farley]

OK, I would not assume that is a valid test. One cannot assume that a refractometer standard can be used with the same values on a hydrometer. The reason is the standard need not be seawater, just something that matches the refractive index of 35 ppt seawater. That fluid might not match the specific gravity of 35 ppt seawater, and in fact, if one used my DIY standards (which some companies may now use), they would be different (not as much different as you observe, but significantly different):

Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.htm

 

[flyfisher2]

Okay... let me try and get this right...

Just got back from Walmart with the Morton's.

Dunked both Coralife hydrometers in the aquarium and I'm getting 1.025 and 1.0255 respectively.
After calibrating the refractometer with the Morton's solution I'm getting 1.022. Exactly the same reading as with the calibration fluid from LFS.
Note: I had contacted coralife and they sent me the second hydrometer after I explained I was Having problems with the initial one I purchased. As you can see they are both very close to each other in their readings although higher than the refractometer once properly calibrated.
I found it interesting that calibrating the refractometer to '0' with RO/DI water yielded the same exact reading as the hydrometers.

 

[Randy Holmes-Farley]

Can you tell me exactly what you did with the Morton's salt to make the standard?

 

[flyfisher2]

I opted to follow your directions as best I could using a Pelouze Model SP5 digital scale
I placed an empty cup on my digital scale.
Reset the tare
Set to grams
added RO/Di water until I obtained a 96g reading
Added Morton's Iodized salt until I obtained a total reading of 100g
Mixed until dissolved
Verified the 100g reading
Added three drops to refractometer and calibrated to 35ppt after waiting 30 seconds

Is my method close enough or should I have gone by volume?

 

[Randy Holmes-Farley]

Mass is the best way, but are you suggesting you added 4 full grams of salt? Does the scale read to tenths or hundreths of a gram?

It should be 3.65 grams salt then water to 100 grams total mass for a refractometer.

The proper reading on a refractometer using 4 grams exactly would be something like sg = 1.029.

 

[flyfisher2]

After your last post I decided to attempt the standard by using the volume method.
This is what I did:
4 level tablespoons of Morton Iodized salt + 1 level teaspoon
One 2.1 liter 7UP bottle (I hope the choice of drink doesn't alter the results)
Filled bottle to brim with newly produced RO/DI water
Poured water from bottle into clean bucket
Stirred in Mortons salt
Calibrated refractometer using this mix
Tested aquarium water
Results:Coralife hydrometer 1 1.025
Coralife hydrometer 2 1.026
Refractometer 1.024

 

[flyfisher2]

I'm afraid the scale is not that accurate.
I added water first so I reversed the process.
Based on the lack of accuracy on the scale I don't think that would have made much of a difference?
I did go the mass method with slightly different results as you can see in my last post

 

[Randy Holmes-Farley]

That result by volume looks a lot better.

 

[flyfisher2]

It sure does... I just hope it's accurate. The 2LT bottle is not exactly 2LT as you pointed out in your article.
I'm going to try and find a more accurate gram scale.(Becoming obsessed) I'm trying to find one locally. Maybe If I go down to the shady area of town and ask the drug house if I can borrow theirs? lol

 

[Randy Holmes-Farley]

:lol:

You could use the gram scale to measure the water volume. How high does the scale go?

 

[flyfisher2]

looks like 2.25 kg

 

[Randy Holmes-Farley]

OK, so you'll do better to measure out

79.3 g of salt (79 g if you can only read to 1 g precision)

and dissolve it in

2104.4 g of pure fresh water (2104 g)

That solution is appropriate for calibrating a refractometer at 35 ppt or sg = 1.0264.

 

[Percula9]

Why don't you get some pinpoint solution from marine depot. See if this solves the problem. What was the LFS calibration solution?

 

[flyfisher2]

I just got back from That Fish Place where I picked up pin point solution. I also got what I thought was a great deal on a Milwaukee EC Meter-Model SM301. I haven't opened it yet. Trying to get some info on it.

 

[flyfisher2]

Why don't you get some pinpoint solution from marine depot. See if this solves the problem. What was the LFS calibration solution?

The solution was their own brand and had nothing on the bottle but instructions for use as I posted above.

 

[flyfisher2]

OK, so you'll do better to measure out

79.3 g of salt (79 g if you can only read to 1 g precision)

and dissolve it in

2104.4 g of pure fresh water (2104 g)

That solution is appropriate for calibrating a refractometer at 35 ppt or sg = 1.0264.

Randy I'll try this tomorrow. I'm dead right now and need some sleep

You know anything about the Milwaukee Conductivity meter I mentioned?

 

[Randy Holmes-Farley]

Unfortunately, that meter won't read conductivity high enough to gauge the salinity of seawater. For that you need to get to at least 53 mS/cm = 53,000 uS/cm, and that one only goes up to 1990 uS/cm. It would be good for monitoring an RO/DI, however.

 

[flyfisher2]

OK, so you'll do better to measure out

79.3 g of salt (79 g if you can only read to 1 g precision)

and dissolve it in

2104.4 g of pure fresh water (2104 g)

That solution is appropriate for calibrating a refractometer at 35 ppt or sg = 1.0264.

Followed your instructions as closely as possible and calibrated to this mix.

Here are my results:

Refractometer using this mix 1.025
hydrometer 1 1.0255
hydrometer 2 1.0245
Refractometer using Sybo calibration 1.0255

The LFS calibration fluid showed 1.030 after I calibrated to your DIY mix so thats just way off.