Refractometer questions

[angler man]

I use a coral life hydrometer to test my water and I noticed a significant fluxuation in the readings. I could test the water with a reading of 1.022 and test again and get 1.025. So I decided to buy a refractometer, I calibrated it using distilled water and it's giving me crazy readings. It's coming up with a SG reading of 1.034 and a salinity reading of 45 ppt.
I decided to re-zero the unit and I reajusted it with even different results. It came up with a SG of 1.028 and a salinity reading of 37.
Could I have recieved a bad refractometer? It was one of those 40 dollar units. How can I make sure that this unit is reading accurately?

 

[matt b]

Originally Posted by Angler man
http:///forum/post/2532550
I use a coral life hydrometer to test my water and I noticed a significant fluxuation in the readings. I could test the water with a reading of 1.022 and test again and get 1.025. So I decided to buy a refractometer, I calibrated it using distilled water and it's giving me crazy readings. It's coming up with a SG reading of 1.034 and a salinity reading of 45 ppt.
I decided to re-zero the unit and I reajusted it with even different results. It came up with a SG of 1.028 and a salinity reading of 37.
Could I have recieved a bad refractometer? It was one of those 40 dollar units. How can I make sure that this unit is reading accurately?
thats not a crazy reading if you where using a hydrometer. cal it with distiled and test and thats your real reading

 

[wangotango]

I don't think that you can match SG to salinity perfectly, as I think SG varies with temperature.
The plastic swing-arm hydrometers are not accurate at all. If you get little bubbles or anything on the arm it with throw off the reading.
Calibrate your refractometer with RO water and make sure it reads zero. Also if it does not have automatic temperature compensation, make sure the water you test is at the right temperature.
-Justin

 

[bang guy]

If you can find 35ppt calibration fluid this is a more accurate way to calibrate a refractometer. I have a recipe for making calibration fluid using table salt and RO water, I'll see if I can find it.
Another way is to find someone with a TDS meter to test your saltwater and then adjust your refractometer to whatever the TDS meter shows.

 

[angler man]

Originally Posted by Bang Guy
http:///forum/post/2533030
If you can find 35ppt calibration fluid this is a more accurate way to calibrate a refractometer. I have a recipe for making calibration fluid using table salt and RO water, I'll see if I can find it.
Another way is to find someone with a TDS meter to test your saltwater and then adjust your refractometer to whatever the TDS meter shows.
I have a in-line TDS meter that I have yet to install on my RO/DI unit, can I somehow use this?

 

[bang guy]

Originally Posted by Angler man
http:///forum/post/2533270
I have a in-line TDS meter that I have yet to install on my RO/DI unit, can I somehow use this?

Probably not. Most of these meters are low-range so they can be accurate to 0tds. You'll need one that can go up to 60,000tds.

 

[gmann1139]

Another way to check your refractometer is to bring it to a LFS or another hobbyist and test the same water with theirs.

 

[angler man]

Originally Posted by Bang Guy
http:///forum/post/2533512
Probably not. Most of these meters are low-range so they can be accurate to 0tds. You'll need one that can go up to 60,000tds.
How much is a TDS meter?

 

[angler man]

Originally Posted by gmann1139
http:///forum/post/2533598
Another way to check your refractometer is to bring it to a LFS or another hobbyist and test the same water with theirs.
My LFS uses those crappy swing arm types, so I'm not too confident in their readings either.

 

[bang guy]

Originally Posted by Angler man
http:///forum/post/2533631
How much is a TDS meter?

Typically the high range meters are $50 - $100. You only need to use it once to calibrate your refracometer so just try to borrow one.

 

[angler man]

Originally Posted by Bang Guy
http:///forum/post/2533696
Typically the high range meters are $50 - $100. You only need to use it once to calibrate your refracometer so just try to borrow one.
Are there any downfalls to those pin point moniters?

 

[jefnmichele]

The refractometer needs to be at the correct temp, not the water.
If the refractometer tells you that it is cal at 78 degress, the temp of the drop of water you place on the glass is not as important as the temp of the meter. This is the reason that the heads of the meters, the good ones at least are metal, to hold the temperature.
The drop of water will absorb the temp of the meter.
Im not talking testing ice cubes. within reason