Do refractometers go bad?

[gregr]

I've been using a refractometer to keep tabs on my tank's salinity. I calibrate it using ro/di water. Recently I made up some saltwater for a friend that just bought a new tank and she told me the water was 1.021, measured on three different hydrometers (all three gave almost exactly the same reading). I know hydrometers cannot be fully trusted but three different ones giving the same reading... I'm worried now If it were off less it wouldn't bother me but that is off a lot! Anybody had a problem with their refractometer? I've never heard of them going bad before.

[Chasman]

One thing you can do is purchase a bottle of "Pinpoint Salinity Calabration Fluid" to check your calibration. You can get this premixed at 35ppt or 1.0264sp. Your refractometer as well as mine is calibrated for salinity NOT ocean water. Using the the fluid above (which is ocean water consentration) you can guage where your refractometer reads it. You can reclaibrate it if you want, or you can see where that reads and use that as your benchmark. Refractometers are pretty basic instruments unless droped or subjected to unusual amounts of moisture.

"The Filter Guys" sell that specific fluid, as does Marine Depot. It's an easy way to check things out.

Chasman

[gregony]

Specific gravity changes with temperature. Did you take that into account? If so, then I guess refractometers do go bad, or at least out of cal. Everything goes out of cal sooner or later. Everything goes bad sooner or later.

[gregony]

Oops, after I typed that I went to go double check. It changes, but like, not very much, so I'd go with you're refractometer being out of cal.

[Chasman]

The fluid is rated at 77degF. It comes with a temperature conversion chart as well. You can check it out at Welcome to American Marine Inc.

Or you can just throw the thing out and buy a new one and wonder if it's any better than the old one.

I was just trying to be helpful and save a few bucks.

[gregr]

Thanks you guys for the help. Saturday I'm taking some water and my refractometer to a fish store and we'll see what's up. If they have some of that calibration fluid I'll get it. If the refractometer is bad then I'll get a new one but... how could something so simple be bad? It hasn't ever been dropped and it's kept very clean in a nice dry container.
What if any long term effect would running a reef at 1.021 have? I use an auto top-off system so the SG is consistent at least. Corals are looking great and growing well. Calcium reactor and kalk drip keep things in balance. Alkalinity is usually around 10-11 and calcium 420-430, magnesium 1350 and pH ranges from 8.1-8.3. Hair algae has been a problem though not for the last few months. I would love to blame the hair algae on low SG

[gregony]

If the refractometer is bad then I'll get a new one but... how could something so simple be bad?

Never, ever, underestimate the incompetence of others. As a repair technician, my entire existence, my home, my car, my dog, and yes, my reef tank is dependent on the failures of others. As a wise man once prosed "What is the difference between genius and idiocy? Genius has its limitations."

Based on your own experience (assuming you're water really is 1.021) I guess you know what the difference between 1.021 and 1.024 is. I think with salinity, stability is the name of the game. That said, I'd want to get that up, because if it gets much lower, it will be a problem for the corals. There used to be an LFS in Denver that kept track of their SG on their tanks. It varied between 1.020 and 1.026. I think I read the ocean varies from 25 to 38 ppt? Based on location.

[gregr]

Thanks Greg. Well, in this case the incompetence was mine for not trusting the refractometer I brought it to the store and it matched perfectly with their recently calibrated refractometer-- on the sample of my own tank water (1.026) and the store water (1.026). We brought along one of those hydrometers and it read 1.021 on both samples. I know it's not scientific but it's good enough for me.

[gregony]

Ahh, yes, another case of the expensive stuff beating out the cheap stuff. That's actually good. Nothing worse than paying the extra money for the good stuff and getting crap. And now, at least, you've verified your equipment (and more importantly your water). This post is a good one. I've been procrastinating taking my own water in for a second opinion from my LFS for a while now. Thinking about it, I guess you should do that every once in a while as a preventative maintenance kind of thing and this post kind of proves it.

[gregr]

I hear ya.