Check your calibration on your refractometer!!

[npaden]

Well it sounds easy enough, but just a warning to everyone to check their calibration on their refractometer periodically.

I had some top off problems when I was on a long vacation and lost a few things in the tank. I did a few water changes and things still were hurting. 2 months later I was still losing corals.

I've been brainstorming in mIRC to try to figure out what my problem could be and Skeldang in #reefs (JeremyR on RDO) asked how long it had been since I recalibrated my refractometer. I hadn't, just the first time when I bought it over a year ago. I was already setup to do a 200 gallon waterchange and dumped in a bucket of IO salt and it mixed to a salinity of 40ppt according to my refractometer! Double checked with a couple swing arms and they said 1.023 s.g.! Recalibrated my refractometer and it was a full 10ppt off!!! My swing arms were never that far off. The tank was at 25ppt or 1.019 s.g. and had been for at least 2 months.

I don't know if the low salinity for a couple months would be responsible for all my tank problems but I imagine that if a coral was already stressed out the low salinity would just be an added stressor. Once my big yellow leather went while I was on vacation that probably accelerated things along too.

Oh well, just a very long winded post to tell people to make sure and check the calibration on their refractometers at least every couple months.

FWIW, Nathan

 

[liquid]

Same thing happened to me in my 40 gal tank Nathan. I found that my salinity had dropped to 1.020 (was using a swing-arm at the time) and over the course of a couple months I lost a 2 yr old Acro that I grew from a salvaged bleached 1" frag from Harbor, a 16" tall green Nephthea and I almost lost my leather coral that had dwindled from 8" across down to 4" across. It's really freaky to see corals that were once thriving all of a sudden just start withering away. Now that I've got my SG back up to 1.026 everything's perked back up again.

Just for the record, how did you recalibrate your refractometer?

Shane

 

[npaden]

I used distilled water. Some people use RO/DI but the instructions on mine say to use distilled. I also checked it against a couple swing arm hydrometers that I have.

Now that you mention it I remember getting the temperature down to 65 or something when first calibrating it. Might need to do that still. It is auto temperature compensating so I didn't worry about the temperature of the water but it was at 78 and it was about 76 in the house.

FWIW, Nathan

 

[liquid]

So there was no need to do a know salinity to calibrate it? You only had to use distilled water and that's it?

Shane

 

[npaden]

Yeah, you set it to zero ppt using distilled water.

 

[liquid]

marked for archiving

Thanks for the info Nathan! I'm gonna archive this one as it's a topic I haven't seen in our archives yet.

Shane

 

[ReefMon]

Thanks to Randy Holmes-Farley here are some Salinity Standards you can whip up:

Salinity Standards
Here's a compilation of salinity standards that people can make out of dry table salt and water (using a good balance):

If you want an S=35 standard for specific gravity, try 3.7 weight percent NaCl in water at 20 deg C

If you want an S=35 standard for refractive index, try 3.6 weight percent NaCl in water

If you want an S=35 standard for conductivity, try 3.17 weight percent NaCl in water

Happy Reefing!
Glenn R

 

[Anonymous]

Distilled water, not RO/DI, is known to be pure water. It's achieved its distilled status by distillation doncha know. Good heads up, though I'm surprised that your swing arm x) hydrometers are so good. I love to float the glass tubey thing!

 

[Anonymous]

The definition of "pure" water is not something that is fun to get into...

Anyway, for most linear transducer, both slope and intercept are calibrated. This is the case for pH meter, for example, and two different fluid is used to "calculate" the slope and intercept (Y=i+s*X). However for optical refractometer, only the intercept can be adjusted because of the way it is constructed. Therefore, "pure" water is used to calibrate the refractometer. After calibration, if you ran a sample with know refractive index (refractometer is a device for measure refractive index, not salinity, but both are close enough in NSW that it is almost interchangeable, among density, conductivity, and other inherent properties), you will be able to find out how well constructed your refractometer is. Crapy one will give you a bad reading, while an analytical unit will give you consistant, accurate result.

 

[ReefMon]

FWIW,

I get 1.000 on distilled, RO/DI and tap water as the amount of solids IMO are insufficent to show any refraction.

Glenn R

 

[npaden]

Heh,

You've never tested my tap water!

470 TDS - I'll check to see what it shows on the refractometer tonight.

 

[Anonymous]

One has to have pretty bad tap water to be able to detect it using refractometer. The difference between tap, RO, distilled, and RO/DI is almost undetectable with optical refractometer.

For "almost-pure" water, conductivity method is better than refractive method.

 

[-JB]

Nathan,

What refractometer was it? I ask because I just checked my refractometer last month with distilled water and it was still dead on, last time I checked it before that was about a year prior. I am using one of the Aquamarine refractometers that cost me like $110, 2 1/2 years ago.

 

[Reef Guy11]

I have the Portable Refractormeter RHS-10ATC from MarineDepot that has a screw type Calabration on top were you adjust it for there. Do you still have to recalibrate it with that type too.

 

[npaden]

From my understanding pretty much all of the refractometers in the hobby are coming from the same source in China. My refractometer instructions say it is a RHS-10ATC as well.

It is the kind that you use the little screwdriver to calibrate. I have no idea why mine would lose it's calibration, but it looks like it would be a good idea to check it at least every few months just to be safe.

FWIW, Nathan

 

[Reef Guy11]

Hey thank i will do that.

 

[EmilyB]

I still use a SeaTest Hydrometer that has been in agreement with the refract. So at least I have a warning if one looks weird.

 

[-JB]

Nathan, Was is one of the less expensive models that are all over now or one of the original $110-120 models? Just wondering if the less expensive ones are showing a need to recalibrate occasionally.

 

[mhurley]

Nathan,

I did the same darn thing when I recently set up my 375. I was killing SPS left and right and couldn't figure out why, all my parameters were ideal. SG was at 1.025 on my 1 month old refrac (I calibrated it when I opened it, and never thought about it again). Finally, I rechecked the calibration and it turned out I was actually at 1.016. That was a lot of fun....Painful and expensive lesson learned. I lost at least 6 Dr. Mac frags that I purchased.

Mike

 

[npaden]

JB,

Yes, I purchased mine for only $50 at www.diyreef.com - They are down to $43 there now.

However, from talking with the owner there (who is a great guy and knows his stuff - Saltshop on Reefcentral) these are the identical refractometers that were being sold a few years ago for $100 - $200.

The reason they are so much less expensive now is that the volume has increased dramatically for them. I guess some problems could arise from the higher volumes being produced but I believe it is the same exact manufacturer still making these. Mine came in a nice blue plastic case with the little screwdriver and a dropper inside and an instruction manual in english. A local reefer purchased one of the $100+ ones a couple years ago and if you put them side by side you wouldn't be able to tell the difference. I could be wrong though!

However, I would recommend no matter what make or model your refractometer is it needs to be at least checked every few months.

I'm slowly bringing my salinity back up and things are already starting to look better. (At least in my mind anyway - it could just be wishful thinking, I'm sure the 200 gallon waterchange didn't hurt anything either) I have it up to 29ppt and am bringing it up about 1ppt per day.

Oh well, FWIW, Nathan