My refractometer is way off when testing with Pinpoint 53mS calibration fluid

[Randy Holmes-Farley]

If I get the bottle of stuff am I right that the process is as follows:

1. Use RO water and set to zero.
2. Use the calibration fluid and if it does not read 1.026, set it to 1.026, and in the future use that to calibrate to 1.026.
3. Test tank water and adjust with topoff as necessary.

That sounds like a good process to me.

[ostrow]

Well, this dummy wisened up. I am a prof at a univ. Called someone in the chemistry dept. Have refractometer with me. Calibration to happen soon, against some purty reliable equip.

[ostrow]

Question: Randy , why is your solution recommendation at 36.5ppt?

Chemistry Prof over here mixed 35ppt/1.026 solution for me. My black RHS-10ATC measured it as just below 1.023/33ppt.

So, now I have a bottle of 35ppt and I can calibrate with RO/DI 2.5 lines or so above the zero mark.

I always tried to keep my tank at 1.0255. I guess it was really around 1.0225.

Sigh. At least now I know.

And we always wondered why our snails suffered such disturbing die-off rates... is this a reason? Or do those with properly calibrated tanks have the same death rates?

[sjm817]

Its interesting that so many people got a refractometer as an improvement over their "inaccurate" hydrometer. It turns out unless you calibrate it first, you are no better off.

[ostrow]

Well, it was supposed to be easier to calibrate, with RO/DI to zero. And has more presice measures and easier read.

BUT yes, it needs to be calibrated and not against RO/DI either...

Oh well.

[Randy Holmes-Farley]

Question: Randy , why is your solution recommendation at 36.5ppt?

The various salt solutions in my article should exactly match 35 ppt seawater.

What exactly did he mix for you?

[ostrow]

35ppt using nacl.

From your article:
This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water.

That isn't 35ppt.

[Randy Holmes-Farley]

Correct. The NaCl solutions in my article are designed to match 35 ppt seawater in terms of refractive index (what you used), specific gravity,or conductivity. Since seawater has other salts in it, 35 ppt NaCl does not have the same exact properties as 35 ppt seawater, so the NaCl solutions are adjusted in concentration to match 35 ppt seawater.

Its interesting that so many people got a refractometer as an improvement over their "inaccurate" hydrometer. It turns out unless you calibrate it first, you are no better off.

I have long argued against this, but without good standards available, most folks just believed their refractometers were accurate.

[ostrow]

Randy:

So this creates some puzzlement for me as to how to use this DIY solution. Am I right here:

If we mix it at 36.5g/100ml, in fact that will be 36.5ppt. But we are to pretend it is 35 and calibrate the refractometer to read that. Then measure the tank and see what we get and adjust the water as needed until it also reads 35.

Right?

[Randy Holmes-Farley]

36.5 grams per liter, not per 100 mL.

From the article:

This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water.

But we are to pretend it is 35 and calibrate the refractometer to read that. Then measure the tank and see what we get and adjust the water as needed until it also reads 35.


Exactly.

[ostrow]

3.65. Yeah. Darn decimal point. Why can't it sit still.

Ok, so we are to miscalibrate with the homemade solution so that we read right with the tank. And ignore the RO/DI zero calibration altogether.

I think some peeps aren't getting this, they are mixing the stuff and giving out a "whoa!" when their measure is way off. Of course it'll be off. In fact, the 3.65 will read at 36.5ppt. It's supposed to read that.

Ok, thanks.

[Randy Holmes-Farley]

Ok, so we are to miscalibrate with the homemade solution so that we read right with the tank. And ignore the RO/DI zero calibration altogether.

Well, I wouldn't really call it miscalibrate. I'd call it a different calibration point. It was miscalibrated by using the RO/DI if it read my solution wrong.

I think some peeps aren't getting this, they are mixing the stuff and giving out a "whoa!" when their measure is way off. Of course it'll be off. In fact, the 3.65 will read at 36.5ppt. It's supposed to read that.


Really? I'v e not encountered many folks that seemed to think that, but I'll pay closer attention, and make it clearer in my upcoming refractometer article (comes out Dec 5 or so).

[ostrow]

Originally posted by Randy Holmes-Farley
[B]Ok, so we are to miscalibrate with the homemade solution so that we read right with the tank. And ignore the RO/DI zero calibration altogether.

Well, I wouldn't really call it miscalibrate. I'd call it a different calibration point. It was miscalibrated by using the RO/DI if it read my solution wrong.

Let's see if I understand this. If the RO/DI calibration is right, then it will read your solution as 36.5ppt. But if it does not read that, then we should calibrate with your solution at 35ppt so that we accurately measure seawater.

I have no idea why this is right, but I think it is.

[Randy Holmes-Farley]

The problem is that with RO/DI calibration, the assumption is that the device is made perfectly, and if it is, it will read my solution as 36.5 ppt if it is designed for sodium chloride and 35 ppt if it is designed for seawater.

If it is made improperly, as many apparently are, it could read just about anything.

[ostrow]

I see... but, ummm, so what then does the test tell us in the end? It seems not much? Let me explain:

I had a new batch made to your formula. I set to zero with RO/DI, then tested with the solution. But so what? I set the line to 35ppt. But this may have been a mistake it seems. Should I have set to 36.5 in case it was made for NACL? But what if it was made for seawater? To 35? But what if it wasn't? Even if I knew it was made for NACL, and I set to 36.5, will it accurately read seawater then?

I put the line at 35ppt for your 36.5ppt solution. But from your post above, this is not necessarily the right thing to do.

With each post I get confused about something different!

[Boomer]

Ostrow

Not to confuse you anymore but here is some more info left out.

Chemistry Prof over here mixed 35ppt/1.026 solution for me. My black RHS-10ATC measured it as just below 1.023/33ppt.

Some of these units, RHS-10ATC, have shown to be off that amount you gave from the factory. A good lab grade would have said 35 ppt or 3.5 % in the professors solution of 3.5 % /35ppt NaCl. The normal off-set for seawater is -15 "units" when calibrated to 35ppt NaCl. Meaning, that a refract used for seawater, when calibrated with a 35 ppt NaCl solution will read, not 35ppt but 33.5 ppt when you put real seawater on it that is know to be 35ppt .

Some of these RHS-10ATC, by accident, have a manufacturing calibration error, which ends up reading correct in seawater, without out calibration. Yours may be one of them, since it reads low in a 35 ppt solution.

When a NaCl refract has the screw turned, such as using Randy's DIY or a real seawater std and you turn that screw from the 36.5 to give a reading of 35 ppt on the refract and then put some RO/DI water on it, it will be below the zero mark by at least 1.5 ppt. Reason, the scale is a NaCl scale and not a seawater scale, which has different spacing between the numbers. Think of a ruler and yards vs meters. A real seawater refract will not do this and can be calibrated with RO/DI to zero . And if you put on some of Randy's DIY 3.65 %/36.5ppt NaCl it will read 35ppt, without turning the screw.

Next week thefilterguys.biz will be selling these real seawater refracts about $100. There are only 3 real hand-held seawater refracts made, @ $100, $200 and -$500 ( which has been discontinued as of 2 months ago but they still have a replacement, based on a std, for about then same price, which has multi-calibration points.

I put the line at 35ppt for your 36.5ppt solution. But from your post above, this is not necessarily the right thing to do.

As you do not have to. Once you know where you are at you could just adjust it in your head. So you put on some of Randy's DIY 36.5 . Lets say it reads 36.5 and you know from Randy and the normal error correct is 15units. When you mix up a seawater batch you want the refract( no turing screw to 35ppt) to read 36.5 which you know = 35 ppt NSW. This way, in most cases, you can still zero out the refract in RO/DI.

What Randy is doing here is making the refract work as if it was seawater. A 36.5 ppt NaCl solution has the same exact (RI)refractive index number as seawater @ 35 ppt.

Look through this and look at Table 2, where RI = 1.3394

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

[ostrow]

D*** it Boomer, I knew you would come in here and do that!

Ok, so I'm not smart enough to adjust it in my head. I'll forget or not trust it.

Randy said above to turn the screw so it reads 35 when I mix 36.5 NACL. When I do that, RO/DI puts the line below zero. By roughly htose 15 units it appears.

But now when I mix the saltwater up, or test the tank, what do I want the refracto to read? I want my tank at 35ppt. But having turned the screw, when it shows 35, that is in fact 36.5.

So, the, I DON'T want to turn that screw right?

Can one of you make the next post for dummies like me?

Step one I got: make the 36.5 solution.

Step two: on the refracto, set the line to ????

Step 3: tank and makeup water should be mixed to read ????

I need those question marks filled in.

My brain hurts. I've always been bad at chemistry.

[Boomer]

Randy said above to turn the screw so it reads 35 when I mix 36.5 NACL. When I do that, RO/DI puts the line below zero. By roughly htose 15 units it appears.

That is fine to do it that way

OK

Step one I got: make the 36.5 solution.

Ans.........OK

Step two: on the refracto, set the line to ????

Ans.........It make no difference what it said with the 36.5 solution drop on the refract. Turn the screw, set the line, untill it reads 35 ppt on the refract. If it reads 36 with the 36.5, just turn the screw until it reads 35......done. If it read 34, turn the screw until it reads 35 .....done

Step 3: tank and makeup water should be mixed to read ????

Ans...........The 35 it now says on the refract = NSW @ 35 ppt what you want the tank at.

I need those question marks filled in.

Filled in

[ostrow]

like i said, i'm a dummy

[cham]

Just ordered two bottles of the pinpoint stuff.

I hope its not on national back order after this thread. Pinpoint needs to pay Randy & Boomer royalties.

Will the price be 4.50 next week or month?

[ostrow]

This is my 4300th post.

Folks, I'd have to say that probably 4200 of them are me asking people to repeat things that everyone else on the planet already understood ages ago. Re-reading this thread, I realize that I was certainly on the mark in my 4299th post.

Thanks for the tolerance!

My tank tested at 33ppt. Not terrible, but not where I wanted it. In the process of fixing it now. One point at a time!

[MJAnderson]

OK, I've made 2 batches of the salt solution and gotten 2 different results. Does the Pinpoint fluid work? I'm starting to think that the measuring cups are conspiring to mess with my brain.

[sjm817]

Originally posted by MJAnderson
OK, I've made 2 batches of the salt solution and gotten 2 different results. Does the Pinpoint fluid work? I'm starting to think that the measuring cups are conspiring to mess with my brain.

LOL, read my posts and Billy's on the 1st page. Sounds like we are all "measuring cup challenged". The Pinpoint fluid takes that problem out of the equation.

[Randy Holmes-Farley]

I had a new batch made to your formula. I set to zero with RO/DI, then tested with the solution. But so what? I set the line to 35ppt. But this may have been a mistake it seems. Should I have set to 36.5 in case it was made for NACL? But what if it was made for seawater? To 35? But what if it wasn't? Even if I knew it was made for NACL, and I set to 36.5, will it accurately read seawater then?

You are making this too complicated. My salt solution matches 35 ppt seawater. Nothing else matters. If you use it to calibrate the refractometer to 35 ppt, you will be all set. There is no situation where you should do anything else.

K, I've made 2 batches of the salt solution and gotten 2 different results. Does the Pinpoint fluid work? I'm starting to think that the measuring cups are conspiring to mess with my brain.

How different were they?

[cham]

Ok, can I clear the air real quick. Its gone back and forth a couple times.

The pinpoint stuff will calibrate the cheaper "blue handled" refractometer correctly to 1.026 and make my cheap unit pretty accurate for testing my tank?