Refractometer Help

GoGoGeeba · Jul 25, 2016

I recently purchased a Refractometer. According to the instructions it says to use distilled water to calibrate. I know that's not the most accurate but I do not have any calibrating solution. I calibrated it using distilled water and it was at 0. I tested my aquarium water yesterday and it was at 1.03. I added approximately a gallon of R/O water and today it says it's still at 1.03. I have a 60 gal all in one. I checked with the Hydrometer that I have and it says it's at 1.024-1.025. I consistently do water changes every week with sea water. I top off with store bought R/O water. (I am saving for a RO/DI unit). Which one should I trust? How do I know if I am doing the Refractometer right? Any suggestions? Thank you.

Jimbo662 · Jul 25, 2016

Take the refractometer to one of your LFS's and have them check it. I've always heard the hydrometers aren't accurate enough. Adding one gallon of water to a 60g tank isn't going to change the salinity very much at all.

GoGoGeeba · Jul 25, 2016

Here is my method of topping off with fresh water. I did a water change a while ago and tested the water with a hydrometer, before I had a Refractometer, and it tested 1.025. I drew a line with a sharpy where the water level was at. After 24 hours I drew another line, which was approximately 1.5in lower. So every time the water level gets to the lower line I add water until it gets to the top line. Is that not a good way of judging how much fresh water to add?

moreef · Jul 25, 2016

get some calibration solution its cheap and the only way to go imo

moreef · Jul 25, 2016

btw I also used distilled water to calibrate until I noticed my ALK/CAL was really low and couldn't understand why till I realized my tank was at 1.020

DLHDesign · Jul 25, 2016

Calibration solutions typically won't target 0.00 - they'll be for around the area you are looking for. My solution is 1.030, for example.

After calibrating mine, I usually test it with some RO/DI water as a secondary test; I'm looking for a value of 0 and always find it correct. While having the calibration solution is ideal, you should be able to use RO/DI water and target 0 to get an accurate reading.

Be sure to rinse off the lens of the refractometer with RO/DI (or tap) water and then dry it. If you're not seeing a clear line in the viewer, you might need to aim it at a stronger light source to get that.

Jimbo662 said:
Take the refractometer to one of your LFS's and have them check it.

Take some of your water while you're at it and have them test that as well.

DLHDesign · Jul 25, 2016

OH - and make sure that your refractometer is actually FOR saltwater. Brewing refractometers look identical to saltwater ones, but will not give you an accurate reading of saltwater (brewing is about sugar; sugar refracts differently than salt).

Note: Brewing refractometers will read low. A read of 1.025 on a brewing refractometer will be around 1.040 or so on a saltwater one.

GoGoGeeba · Jul 25, 2016

DLHDesign said:
OH - and make sure that your refractometer is actually FOR saltwater. Brewing refractometers look identical to saltwater ones, but will not give you an accurate reading of saltwater (brewing is about sugar; sugar refracts differently than salt).

Note: Brewing refractometers will read low. A read of 1.025 on a brewing refractometer will be around 1.040 or so on a saltwater one.

How do I know if I got the correct one?

DLHDesign · Jul 25, 2016

GoGoGeeba said:
How do I know if I got the correct one?

It should say "Salinity" or the like in the viewer somewhere (mine is bottom-center). If you see "Brix", then it's a brewing one.

GoGoGeeba · Jul 25, 2016

Ok it says Salinity. I ordered some calibration fluid and I'll see what happens.

Salty1962 · Jul 25, 2016

You should use 35ppt calibration fluid to calibrate your refractor. Most major online vendors carry it.

gig 'em · Jul 25, 2016

So you're drawing a line in the sump and refilling with freshwater whenever it drops? Are you using a protein skimmer in your system? Is it running "wet" and pulling a lot of liquid out? This method of removing water via skimming and from evaporation and replacing it indiscriminately with fresh can skew your salinity over time if you're not careful. I would get calibration solution and compare it against a known standard like a friends or one at tour LFS.

FishLover01 · Jul 25, 2016

First of all, I wouldn't be using distilled water for calibration purposes. It will always test at 0 on a refractometer. I use calibration fluid and it's standard is 1.026 . Since your salinity is probably between 1.024-1.026 it makes sense to use the fluid because it's in the same range that your salinity content should be. Also, some refractometers need about 45 seconds to adjust to temperature before you read the results. Hope this helps.