Need a Favor in Central Tucson (refractometer calibration)

[Tanque Verde]

Last time I performed a water change, I dropped my refractometer. Today when I used it again, I discovered that the readings were all out of whack. I recalibrated according to the instructions, but it still seems squirrely, and now I've got doubts about both my refractometer and my tank salinity.

I'm absolutely slammed with work and I can't get over to the Oracle stores today, so I am wondering if anyone in Central Tucson (the closer to Swan/Speedway the better!) would mind me stopping by for ten minutes early this evening to check my water with your refractometer, your water with my refractometer, and otherwise double check my calibration.

Thanks.

 

[Bifferwine]

I have refractometer calibration fluid that you are free to use if you'd like. That would be better than having someone else check your water (their refractometer could be off as well). I live on the NW side of town though

 

[Tanque Verde]

^Thanks, Biff.

Prickles offered to stop by with his refractometer. But I'll be in touch if I can't figure this out. In any event, my refractometer calibrates with distilled water, so I don't know if your fluid would help me out.

BTW, I saw your look alike again. She's driving a rust-brown Mercedes SUV and could be your sister.

 

[Bifferwine]

Calibrating with distilled water can work, but it's not as accurate as calibrating to the fluid, which is the same specific gravity as salt water (1.026 or 35 ppm). Your refractometer could be measuring lower than what the solution actually is, but if you test it against distilled water, you'd never know. Distilled water should show up as 0, so if your refractometer is off in the low direction, it won't show it using distilled water because they don't go below 0 on their scale (at least, mine doesn't).

The refractometer is also less accurate the further away you get from that value, so it may be off by a little bit when you test your tank water. You can calibrate any refractometer using calibration fluid, which you can buy for cheap (it's about $4 a bottle) from a scientific lab store or Ebay.

Here is a good thread about the perils of calibrating with distilled water and discussions of the 'conversion' you have to make to the value you get if you do so!

http://www.reefcentral.com/forums/showthread.php?threadid=1326143

And I need to find out who this creepy twin is. There's only room for one of us in this town. Who wants to drive a rust-brown car anyways?!?!

 

[wsz594]

calibrating with distilled water can work, but it's not as accurate as calibrating to the fluid, which is the same specific gravity as salt water (1.026 or 35 ppm). Your refractometer could be measuring lower than what the solution actually is, but if you test it against distilled water, you'd never know. Distilled water should show up as 0, so if your refractometer is off in the low direction, it won't show it using distilled water because they don't go below 0 on their scale (at least, mine doesn't).

The refractometer is also less accurate the further away you get from that value, so it may be off by a little bit when you test your tank water. You can calibrate any refractometer using calibration fluid, which you can buy for cheap (it's about $4 a bottle) from a scientific lab store or ebay.

Here is a good thread about the perils of calibrating with distilled water and discussions of the 'conversion' you have to make to the value you get if you do so!

http://www.reefcentral.com/forums/showthread.php?threadid=1326143

+1

 

[prickles]

this may be true, but i think it's also only one time use which is annoying. i have a bottle of the fluid for my salinity probe and it's WAY off after sitting a few months in it's bottle. So can you trust your fluid?

Also for those who have done it (I have only done it on my probe, not the refractometer) are you really getting a different reading than when you calibrate with distilled water? If so, by how much?

I may be lazy, but when I mix water, I check the tank water which seems to stay at 1.025, and mix to somewhere between 1.024 and 1.026. If it's just 0.5 more accurate, who really cares? Do you mix your water that closely?

 

[Bifferwine]

Calibration fluid does not go bad. I am a scientist and use it for work all the time. We buy it in 1/2 gallon jugs and it lasts for...well for as long as it takes to run out, which is years? Are you sure it's not your probe going bad? That's more likely than the calibration fluid.

I've checked mine against calibration fluid from my work and a bottle that I bought off of Ebay, and they both read the same. It was .03 off from using distilled water. To some people, the difference between 1.020 and 1.023 may not be significant. I think it is.

I don't match my new water very closely. When I do a water change, I'm doing 10% of the system's volume at the most. Being off by a bit for that small amount of water is not going to make a difference. But if you are treating sick fish using hyposalinity, you'd better make sure your refractometer is accurate. I use my refractometer not only for making up new water, but also for making sure I'm not falling too far behind on top offs. For some reason, my salinity seems to naturally creep upwards. Even if I'm topping off daily, it's not unusual for it to jump from 1.025 to almost 1.030 throughout the month. I don't know why, but I like to keep track of it so I can fix it before it becomes a problem. If that's not something that bothers you, then it is pointless to calibrate using a fluid instead of distilled water.