Comparing hydrometers

Discussion in 'Water Chemistry' started by lillys Grandad, Feb 6, 2012.

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  1. grinder37

    grinder37 Whip-Lash Squid

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    Thank you,but i have a bottle of 35ppt solution coming also as i've read up on that as well,to set at a known salinity.
    But i'm just curious to thier references to distilled vs ro/di,both sould be pure enough to have a known 0 salinity reading and both should be pure enough to not leave minerals,etc to build up on the lense.Why does the manufacturer recommend distilled?
     
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  3. Blue Falcon

    Blue Falcon Fire Goby

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    There was a recent thread about calibrating with ro/di or distilled water vs 35 ppt known solution. The consensus was that mid to high end refractometers could be calibrated with ro/di or distilled water and still be accurate for measuring seawater. But some of the lower end units were a few points off when calibrated with ro/di or distilled water and re-calibrated with 35 ppt known solution. This has something to do with the refractive index and it's always best to calibrate in the range you will be using the device for. Thus, 35 ppt known solution would be best since natural seawater and our reef tanks are very close to that.
     
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  4. lillys Grandad

    lillys Grandad Horrid Stonefish

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    I seen them being used by LA Reef Guys..If I had one I would have done it also :p...I was just doing a water change and decided to shoot a video of this comparison....your using one? do they ever need to be calibrated? They look very fragile....I want one.;D
     
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  5. Mr. Bill

    Mr. Bill Native Floridian

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    LOL

    Yes, that's the only thing I've ever used.

    I have seen them dubbed "scientific grade"; perhaps that's the type of which Corailline spoke earlier? Not exactly sure how one could be calibrated, but yes, they are quite fragile- must be handled gently. :)
     
  6. lillys Grandad

    lillys Grandad Horrid Stonefish

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    These are the good ones...looks like they sell some cheaper models for about 8.00 to 10.00 bucks....and they do refer to testing urine a bunch !! ..gravity is gravity.:eek:

    Hydrometers - Precision Grade, ASTM, Specific Gravity, Light Liquids, 330mm
    The one I seen on LA Reef Guys had a big bulb on one end..??
     
  7. Seano Hermano

    Seano Hermano Giant Squid

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    I never looked into it, but for some reason, I always assumed the lab-grade hydrometers were really expensive. I don't know why. Those are pretty good prices. I kind of want one now, just to have one. lol.

    Thanks for sharing the video with us, lilys grandad.
     
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  9. grinder37

    grinder37 Whip-Lash Squid

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    Thank you Blue Falcon,that cleared it up quite a bit for me,i just didn't understand why when you read instructions it calls for distilled,but when you read up on the forums they say 35ppt,i knew what the difference was,just not why.Thanks for helping me understand this.

    And Mr.Bill,

    I dabbled in FO sw about 25 years ago for a couple years without issue.But back then,floating hydrometers,dolomite substrate with undergravel filters driven by powerheads.For decor there was dead and painted/dyed coral skeletons (even some of those were expensive) and fake plants which was about as good as it got locally and without the internet,corals were not an option,locally at least.All i kept was clowns and damsels along with hermits and turbos.Lol,it's utterly amazing how this hobby has evolved.But the bobbing hydrometer i never questioned as long as it stayed somewhere in the middle,lol.
     
  10. Astrick117

    Astrick117 Stylophora

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    I think this is a great video, but there is just one quick thing I noticed that may have thrown off the results- you held the hydrometers in the air when taking the reading. For proper accuracy, you are actually supposed to put them on a level surface.

    The reason for this is that the scale on the side is only accurate when level. If you tilt it one way or another by even a little you will get varying degrees of accuracy. This is the same reason you don't measure liquids while holding them.

    I agree that a refractometer is more accurate sometimes vs. the cheap hydrometers they sell for saltwater use, but they are a good tool for a quick peek- you just have to keep in mind that they need to be level.

    Also, to an earlier point the bobbing hydrometers are very accurate too. I have used them for home brewing and tested vs. a refractometer and it was dead on.
     
    Last edited: Feb 7, 2012
  11. billielewis3

    billielewis3 Gigas Clam

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    haha the refratometer doesnt have to be level because it has a plastic flap that keeps teh water from moving, and you hold it up to a light and look through the eye piece and the where the water splits is where you take the reading. if youve never use'd or seen one before i know my discription makes no sense at all but thats how it works.
     
  12. Inertiatic

    Inertiatic Bubble Tip Anemone

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    I definitely agree. Hydrometers are only accurate if all the right steps are taken. I know with mine if I tilt it, don't fill it to the fill line, or dont tap off any air bubbles off the needle, my end result is way off.

    I've had a LFS compare results with their refractometer and the results were the same. Just make sure to take care of your hydrometer. I primed mine in saltwater for 24 hours before I used it for the first time and I rinse it with freshwater after every use.