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Refractometers and Salinity Measurement

Discussion in 'Hardware' started by jahmic, Apr 3, 2014.

  1. jahmic

    jahmic Shark M.A.S.C Club Member

    Do you like to calibrate your refractometer with RO/DI water?

    This article should convince you otherwise.

    Would you like to DIY your own calibration fluid?

    This article makes it easy.

    I've been making my own calibration fluid for the past couple years...and have a couple notes on the DIY article above.

    • Whether you attempt the DIY instructions by volume or by weight...in either case it's unlikely that your solution will be spot on. You have a few options to remedy this:
      • Option 1: Make 3 small batches, measure the salinity. If the salinity of each sample is close (.002-.003), mix them all together and you should be close enough.
      • Option 2: Make 3 small batches, measure the salinity. If 2 samples are within range and one is way off...toss that one and mix the other two. Again, you should be close enough. If all 3 batches vary by more than .003 (eg you measure 1.021, 1.025, and 1.029), try again and be more discerning with your measurements.
      • Option 3: Make a batch, and test it against commercially available calibration fluid. Borrow some from a friend, stop in at your LFS...whatever works. If you do plan on just making 1 batch, I'd recommend you bring your refractometer to your LFS, kindly ask them to calibrate your instrument, then bring it home and try to get your DIY solution to match. The nice thing about this method: if you use a calibrated refractomer and mix your own fluid...you can just test your batch and label it with it's known value. You don't have to make your fluid at 1.026...1.024 and 1.025 work just as well since that is within your target range (for a reef anyway).
      • Personally...I make 3 batches, make sure they all are within .003, mix them together, then test against commercially available fluid to make sure that my measurement is correct.
      • *When I say small batches...keep in mind that the larger the batch you make, the less likely that your resulting calibration fluid will deviate from the expected value. I usually make 3x 1 liter solutions (1000ml)
    • Store your fluid in a respectable container. Pee cups won't cut it...you will get evaporation, and the calibration fluid's actual salinity will slowly rise. After about 8 months I saw my calibration fluid rise by .003 when stored in a pee cup. The rate that your fluid "goes bad" will depend on the temp and humidity where you stored it...mine was in a dark cool cabinet and still fluctuated in the pee cup. I purchased a bulk order of 10ml eye droppers on ebay...but you can find similar containers at the dollar store.

    • The article recommends using regular iodized Morton table salt. Table salts contain anti-caking agents which, although soluble in water...still leave me paranoid. It shouldn't effect the refractive index, and they are supposed to be soluble...but I attempted to make the solution with table salt on 2 occasions, and both times I ended up with sediment that precipitated out of the solution after a couple months. Instead I used natural sea salt that's free of anti-caking agents. It's cheap enough, and I keep it in my house for other uses anyway...looks like this:

    Last edited by a moderator: Apr 3, 2014
  2. jahmic

    jahmic Shark M.A.S.C Club Member

    If anybody is interested in making their own calibration fluid...I will have some bottles of 1.025 available at ReefEd that you can take home and test your sample against. Also feel free to grab some if you're still calibrating with RO/DI. :)
  3. Ghxst

    Ghxst Cuttle Fish

    Thanks for the info, along with all the other cool stuff you post. So bummed I have a geology trip the same day as reefed, last year was great. I will be trying this.
  4. Balz3352

    Balz3352 Marlin M.A.S.C Club Member

    Gonna have to grab one.. I only have done ro/di thanks for the article!
  5. djkms

    djkms Shark Platinum Sponsor M.A.S.C Club Member

    I make my own calibration fluid with Mortons Iodized salt. The first time I made it I just used regular salt and it went out of solution after a couple days. I went to the store and made sure to get Iodized. I haven't had a problem with it going out of solution yet (been a few months now). I make it with 0 TDS RO/DI water and use grams scales to measure the water weight and salt weight.

    I use this to weigh the water (161g):

    and this to weigh the salt (6.20g):

    2 digital scales for around $20 shipped (if your a Prime member) is kind of a no brainer :D
    (if your not a prime member and would like for me to get them for you, let me know. Paypal over and you will have it in 2 days, guaranteed.)

    I also purchased a gram weight set to calibrate the scales against, they are SPOT on out of the box!

    I keep the solution in a baby bottle with a screw on top, no evaporation for me. I would agree not to use pee cups though.

    btw Thanks Khalis for turning me on to this months ago.
    Last edited by a moderator: Apr 3, 2014
  6. jahmic

    jahmic Shark M.A.S.C Club Member

    Interesting...Morton's gave me precipitation. I wonder if the age of the salt could be an issue since you bought a new batch? My salt container was several years old...since the anti-caking agents in the salt absorb water, I'm wondering if after several years of absorbing water they aren't as soluble in water due to chemical changes. Anybody know enough chemistry to figure that out?

    Thanks for bringing up the scales, Kris...they are cheap enough and make measuring easy. I lucked out with an old lab scale and have a 1000g weight that I calibrate with.
  7. Balz3352

    Balz3352 Marlin M.A.S.C Club Member

    So I missed picking up one of the calibration fluid bottles.... What are my options
  8. jahmic

    jahmic Shark M.A.S.C Club Member

    I'll try to make a second batch prior to the May DBTC.
  9. Balz3352

    Balz3352 Marlin M.A.S.C Club Member

    Sweet hopefully I can make it!
  10. djkms

    djkms Shark Platinum Sponsor M.A.S.C Club Member

    Or you can make it yourself if you have gram scales
    Or I can make it for you if you want to come by and get some (Southwest Denver).
  11. Balz3352

    Balz3352 Marlin M.A.S.C Club Member

    Where abouts in sw Denver
  12. Balz3352

    Balz3352 Marlin M.A.S.C Club Member

    /what's your availability like
  13. djkms

    djkms Shark Platinum Sponsor M.A.S.C Club Member

    Sheridan and Hampden
    I am available weekdays after 5pm and weekends usually after 2pm.
  14. Balz3352

    Balz3352 Marlin M.A.S.C Club Member

    Any chance you're free tomorrow? Night I could make it over to that area at like 6 to 630 if that works for you
  15. djkms

    djkms Shark Platinum Sponsor M.A.S.C Club Member

    Sure thing, I will pm you my info.

    Sent from my Galaxy S4 using Tapatalk
  16. Balz3352

    Balz3352 Marlin M.A.S.C Club Member

    Thanks a bunch again for the solution! Luckily I was right on with my ro calibration! Phew! Thanks
    Btw your tank is gorgeous!
  17. djkms

    djkms Shark Platinum Sponsor M.A.S.C Club Member

    You're welcome and thanks for the compliment :D

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