SG of calgary tapwater

[Pescador]

If anyone wants to check their refract I went back through the thread on calibration and found the steps.

Calibration with RO first and then check with the Pinpoint 53.0ms fluid.

1. First calibrate the refractometer in pure fresh water. That can be distilled water, RO water, RO/DI water, bottled water, and even tap water with reasonably low TDS. Calibrating with tap water that has a TDS value of 350 ppm only introduces about a 1% error in salinity, causing readings in seawater to read a bit low. So 35 ppt seawater (specific gravity = 1.0264) will read to be about 34.7 ppt, and have a specific gravity of about 1.0261.

This calibration should ordinarily be carried out at room temperature using an ATC refractometer. The directions with some ATC refractometers insist that the calibration be carried out at a specific temperature, but I’ve never understood how that could matter and I would not worry about it. If the refractometer is not an ATC refractometer, then careful temperature control or correction is necessary, and such corrections are beyond the scope of this article.

Calibration is usually performed by putting the fresh water on the refractometer, letting it sit for at least 30 seconds so it comes to the same temperature as the refractometer, and adjusting the calibration screw until it reads a value appropriate for fresh water (e.g., refractive index = 1.3330, salinity = 0 ppt, specific gravity = 1.0000). Normal this step is a quick and easy procedure, and may often be all that is required IF the refractometer has been verified to at least once have passed the second calibration step below. This is an offset calibration, as described above.

2. The second step in calibration should be performed at least once before relying on a refractometer to accurately measure the salinity of a reef aquarium. This step involves testing it in a solution matching the refractive index of 35 ppt seawater (or some similar solution near the range of measurement). Remember to let it sit for at least 30 seconds so it comes to the same temperature as the refractometer. Suitable commercial and do-it-yourself standards were described earlier in this article. Using them, place a drop onto the refractometer and read the value. If it reads approximately 35 ppt or a specific gravity of 1.0264 or a refractive index of 1.33940, then the refractometer is properly calibrated and is set to go.

If it does not read correctly, and is off by an amount that is significant relative to your salinity precision requirements, then you need to recalibrate using this second fluid. I suggest that a salinity error of ± 1 ppt or a specific gravity error of ± 0.0015 is adequate. If the refractometer is off significantly, and you used a do-it-yourself standard made with crude techniques such as coke bottles, a good next step might be to buy a commercial standard.

To correct errors using these seawater standards, simply adjust the calibration screw on the refractometer until it reads the correct values for the standard (35 ppt or a specific gravity of 1.0264 or a refractive index of 1.33940). This type of slope calibration makes the refractometer suitable to read solutions close in salinity to seawater. After such a calibration, refractometers may not read fresh water correctly (although surprisingly, some do).

Again despite the claims in the directions of some refractometers to have the standard at a particular temperaturte, when calibrating an ATC refractometer with this seawater standard, I’d just use it at room temperature.