SG testing differences

[fijiwigi]

Ok so I made my first garbage can full of RO/DI water I mixed the salt in it 24 hours ago. I took my refractometer and placed a few drops of RO/DI water on it and it read 0. So I figure it was calibrated just fine. I then tested my batch of fresh RO/DI saltwater with the refractometer and it read about 1.021 I checked it with my 2 swing arm hydromoters the red sea hydromoter(old one) read 1.016 and the brand new instant ocean hydromoter read 1.026 I was shocked at the difference in readings and am wondering if anyone understands why I could get such different readings. I am assuming to trust the refractometer. But the past 8months i have been trusting my red sea hydromoter if it is off that much I have had way too high of specific gravity the entire time I have been doing saltwater. Any thoughts???

I just tested my tank water with the refractometer it read 1.030(holy toledo) since my red sea hydromoter was off about 5 points my tank is about 5 points too high.

My refractometer is model RHS-10ATC I got it from DR Fosters&Smith

 

[usmcmarc]

I would tend to go with the refractometer...I had the same issue, the refractometer is most probably correct. To verify, take a sample of your water to LFS and have them test with their refractometer.

 

[fijiwigi]

I think I will do so just to be sure.... If the refractometer is correct than I would assume anybody out there without one is probably experiencing unhealthy fish keeping due to poor salinity levels. I think buying a 45 dollar refractometer turns out to be the best investment I could have made out of the 1000's of dollars spent.

 

[ccCapt]

I would definitely trust the refracto more than a swingarm. I highly suggest spending another $4 and get some Pinpoint salinity calibration fluid. You will then have no doubt as to what it really is.

 

[fijiwigi]

So how much of a difference between pinpoint salinity calibration fluid and DI water would there really be. Why use the fluid exactly. If I don't use the calibration fluid will my salt level be off???/ Where do you buy this fluid at?

And I wonder if most hydromoters are off how most of you monitor the SG levels in your tank daily. I guess if you understand how much your hydromoter is off than you could add the difference.. Do any of you have hydromoters that are close to accurate it seems mine are totally wrong.

 

[Kurt_Nelson]

cccapt means a calibration fluid with a known salinity. That way you know for sure that your refractometer measures correct for a salt water solution. Calibrating with RO/DI water only confirms it reads 0 (or 1.000) correct. You can buy the fluid online wherever they sell the Pinpoint (that's the brand name) salinity meters.

With that said though, I don't think most people do this. Probably not a bad idea, and in fact I'll probably pick up a vial of the solution next time I place an order somewhere, just to see how close my refractometer is.

I've heard there are some swingarms more accurate than others. But I'd bet most here use refractometers. It's one of the best investments you can make in this hobby.

 

[cmor1701d]

My refractometer came with a small bottle of calibration soluton. The solution is at 35ppt. The calibration method is to test TODI at 0 and teh cailbration soluton at 35ppt. Then you know that the refractometer is reading correctlly.

 

[fijiwigi]

My refractometer came with a small bottle of calibration soluton. The solution is at 35ppt. The calibration method is to test TODI at 0 and teh cailbration soluton at 35ppt. Then you know that the refractometer is reading correctlly.

Ok it all makes sense now thanks

 

[roka64]

I agree with the rest. I found my hydrometer to be .00500 off of the refractometer. My hydro was reading 1.022 and the refracto read 1.027! Also, the hydros are very picky when it comes to temp. My hydro wouldn't read much salinity right after I ran water (cold) from my tap.