Refractometer

[Sea Keeper]

I got a refractometer from Drs F&S having read it's likely much more accurate than the hydrometer I've been using. In the instructions on calibration its mentions setting it and using it at 68 F. I saw temperature being mentioned with hydrometers but never for refractometers. Now I'm left wondering is this more expensive piece of equipment going to be any more accurate?

 

I've calibrated it using distilled water at room temp and then tested my tank water (78 F) which showed 1.030. The hydrometer shows 1.026.

 

Now I'm wondering should I reduce the salinity because of the refractometer reading?

 

I'm thinking of taking some tank water outside and letting it sit til it gets down to 68 F and see if it changes at all.

 

Should I bother?

[StevieT]

You need to calibrate it with calibration solution to 35 ppt at 77°

 

Then you can test your tank at it's normal temp and have it be accurate. Pick up some solution, you are calibrating it to a salt level, not a zero level.

[Sea Keeper]

So I can test it at tank temp with the solution and then test at tank temp after that? Well that's something I was hoping for! Thank you!

[Sea Keeper]

Oh now I feel stupid. I somehow thought I had the model without temp compensation but I actually do have that one as it is model no. 10ATC (auto temp compensation).

 

Just as an experiment I put a cup of tank water in the freezer and let it get down to 68 F and then used that in the meter and it was exactly the same as with the temp at 78.

 

I thought that 1.030 had to be more accurate anyway as when I would mix my salt (instant ocean) it was supposed to start yielding good SG levels at around 1/2 cup of mix per gallon of water. But I was having to mix as much as 1 whole cup of salt per gallon to get to 1.026 or so.

 

Looks like I need to change some water now.

[psykobowler]

Oh now I feel stupid. I somehow thought I had the model without temp compensation but I actually do have that one as it is model no. 10ATC (auto temp compensation).

 

Just as an experiment I put a cup of tank water in the freezer and let it get down to 68 F and then used that in the meter and it was exactly the same as with the temp at 78.

 

I thought that 1.030 had to be more accurate anyway as when I would mix my salt (instant ocean) it was supposed to start yielding good SG levels at around 1/2 cup of mix per gallon of water. But I was having to mix as much as 1 whole cup of salt per gallon to get to 1.026 or so.

 

Looks like I need to change some water now.

 

Yes, you need to lower that sg by taking some water out and putting freshwater but slowly if you have livestock. I had a similar experience like you using a bubble hydrometer. I was putting more salt than what the instruction said and ended up with the sg of 1.03. Follow the instruction on the bag. The half cup yields about an sg of 1.021.

[StevieT]

I would still get the calibration solution, you are not accurate at a zero level and adjusting the line.

 

float or warm up the calibration solution to about 77° then adjust the refractor. After that you are good at most average temps because you have ATC. I am guessing we have the same refractor.

[Phixion]

Also of note, your tank water (without ATC) will fluctuate salinity at various temps. This is why when you mix salt, you want it to be at the same temp as your tank, otherwise it won't be at the salinity you are going for. But the ATC makes it a no brainer which is nice when just checking your tank salinity levels. Get the calibration fluid like Stevie suggested though. My refractometer is able to be calibrated with 0 TDS RO/DI, but not all can be as accurately as many cheaper ones have deviations in the prism causing bad calibration using RO/DI or distilled water. Better safe than sorry with the calibration solution fluid.

[Sea Keeper]

I'll get the calibration fluid just to be reassured. Thanks for all the responses!