Canreef Aquatics Bulletin Board - SG of calgary tapwater

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SG of calgary tapwater

Can someone with a refractometer let me know the SG of your tapwater? I know the implications of this, but I don't have access to RO/DI water at the moment and am just looking for a general starting point. Thanks.

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Originally Posted by CMarty01 (Post 222243)

There is no SG in tapwater. We take tapwater and mix salt to create saltwater, then test with a refractometer to get the SG.

Unfortunately, there is no answer to your question. You must use tapwater, then condition it with some sort of tap water conditioner, then mix in salt slowly until you reach the desired SG. Most people use an SG of about 1.023 to 1.026. Most commonly 1.025, 1.026.

HTH ..

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Originally Posted by OCDP (Post 222244)

I understand how to mix in salt. But the SG of tapwater is not 1.0000. That is why you must use RO/DI water to properly calibrate a refractometer. I believe tap water should register around 1.002 - 1.003. If you have a properly calibrated refractometer can you test it out and let me know what result you get.

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Originally Posted by CMarty01 (Post 222245)

My mistake...

I can't help you out because I am not at home.. so hopefully another Calgarian will chime in.

Check out this thread on RC

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Who's device and how does it measure it ? You really can not calibrate a refract with pure water. You are just zeroing it out. You need a std for seawater or one that is equal to seawater. Almost all refract, we use, are calibrated to NaCl ( table salt) and that is what you are 'zeroing " it out to. That is not seawater. So most of them are off right out of the box when measuring seawater by .0015 units SG. There have bas been one brand, that many use, that is so far off right out of the box, from what it is suppose to be, that it actually ends up being as if it is calibrated to natural seawater

There are directions for making a calibration solution and for using a 53mv salinity probe solution.

http://reefcentral.com/forums/showth...hreadid=744971

You're over thinking things, the amount of dissolved minerals in the local water is on the high side but not high enough to throw things too far out. Trying to get much closer than .002 or so to "ideal" with the tools we have available is probably more a matter of luck anyway. Obviously you understand that a density measurement starting with anything other than RODI will always be flawed, you can't account for what else is in the water to start with but there are just as many things wrong with trying to measure this with a refractive tool.

My hydrometer will usually measure the SG of the tap water a little above 1.003 but my refractometer (calibrated with RO) will read 1.000. Measuring a mixed salt solution, either brackish or full marine, they are bang on to each other. This can probably be explained by the different way the two tools work, the minerals dissolved in the tap water either do not refract enough light to make the refractometer work or they do it differently than a saline solution would and as such don't result in a useful measurement . In this particular situation I would suspect the hydrometer to be more accurate, if it is a good one.

Give the calibration method Pescador linked to a try, it's probably the best bet you have but in the mean time just mix the salt as directed, it will be close enough.

EDIT: One other thing, I live in the south so my water comes from the Glenmore Reservoir, if your water comes from the Bearspaw it should have considerably less dissolved calcium, 160ppm compared to 220ppm IIRC.

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

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

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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.

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I figured it would be much of a problem but that's a lot less than I thought. Considering that the city's water reports put the TDS < 300ppm even for Glenmore you're at the point that you'd never know the difference, you can't measure that accurately with our gear.

I'm from calgary, and when I mix batches of water from RO/DI and tapwater, the SG's exactly the same, but the alkalinity's/pH is different. I have a calibrated refractometer, too (RO/DI calibration).

do you mean alkalinity?

I always calibrate my using distilled water which it should read 1.000. Well I am from Edmonton, and I think the tap water in the city is around 1.002 or something like that. Checked few times about a year ago.