Help -- Specific Gravity Question

[Cscultho]

What is the SG of RODI water suppose to be? 0?
-swing arm says RODI is 14PPT
-Looking glass is calibrated to 0PPT using RODI

Have two SG measuring devices, swing arm and the looking glass. Both are reading different SG readings and Im not sure which one to use? Ive been using the looking glass one and have my SG set to 35PPT but the swing arm says the same water is 40PPT.

very confused. The looking glass one is what i used to setup my tank and use for all water changes but i wanted a back up device to confirm my readings.

 

[blaxsun]

RODI water? Zero (0). Sounds like the swing arm is off...

 

[Timfish]

I like my instant ocean float type hydrometer over refractometers but air bubbles can easlily give false readings so go with your refractometer. I have seen some off brand float types give consistantly bad readings so be careful of different brands of plastic float type hydrometers. Be sure to keep refractometers and digital slainity readers clean. slat residue left on the glass or sensor can cause errors.

 

[Cscultho]

Thank you for your quick reply. I will use my refractometer as my "gold standard". my swing arm is a Coralife deep six hydormeter. very dis

 

[KStatefan]

Specific Gravity of pure water is 1

 

[Steve2020]

RODI water? Zero (0). Sounds like the swing arm is off...

Are you sure about RODI SG should be Zero? I have read that RODI/Pure water has a specific gravity of 1.000. I have never seen a swing arm that reads down to zero. Ones I have seen the lowest reading is 1.000.

 

[Gill the 3rd]

What is the SG of RODI water suppose to be? 0?
-swing arm says RODI is 14PPT
-Looking glass is calibrated to 0PPT using RODI

Have two SG measuring devices, swing arm and the looking glass. Both are reading different SG readings and Im not sure which one to use? Ive been using the looking glass one and have my SG set to 35PPT but the swing arm says the same water is 40PPT.

very confused. The looking glass one is what i used to setup my tank and use for all water changes but i wanted a back up device to confirm my readings.

The swing arms are generally inaccurate. When you say looking glass, do you mean a hydrometer? If you're talking about a refractometer make sure it is calibrated, I found that mine needs to be recalibrated with 35 ppt solution about once a month.

 

[Cscultho]

I have a refractometer. the instructions said to zero out with RODI water no calibration solution.

 

[sc50964]

I have a refractometer. the instructions said to zero out with RODI water no calibration solution.

I got my calibration solution via Amazon

 

[Cscultho]

I got my calibration solution via Amazon

what is the solution called? I will order right now

 

[sc50964]

what is the solution called? I will order right now

Fritz Aquatics 35ppt (1.026) Refractometer Calibration Solution 2oz.

But it appears to be not available anymore but there are plenty of other brands

 

[Gill the 3rd]

I recently bought this one from amazon:


Ive also used a calibration solution from BRS in the past. Any of them will work fine.

 

[KStatefan]

what is the solution called? I will order right now

You can also make your own using Randy's recipe.

https://reefkeeping.com/issues/2004-06/rhf/index.php

 

[blaxsun]

Are you sure about RODI SG should be Zero? I have read that RODI/Pure water has a specific gravity of 1.000. I have never seen a swing arm that reads down to zero. Ones I have seen the lowest reading is 1.000.

Which is basically zero, yes.