Help! Salinity 40 PPT !?!

[Playapixie]

Salinity YIKES!

I’m sure this was a mistake, but I’ve been calibrating my refractometer with the same bottle of control for 7 years. Recently got an Apex with salinity probe and have been frustrated with calibrating. When I first calibrated it was telling me my salinity was ~40, which seemed ridiculous. Then suddenly a few days later the probe reading dropped to 33, which is what I actually thought it was (ended up a bit off after a series of big water changes after a crash while I was on vacation.) Today I got new calibration fluid in the mail and just about choked when it told me my refractometer was off by 5...and my tank might actually be 40. Everything seems fine...but OMG.

So...slowly correct down to 35 based on the new calibration fluid? Or find yet another calibration standard to check against?

I would have assumed that aging fluid would read higher (due to evaporation); the idea that the old bottle is that much lower is blowing my brains.

What do you think?

I plan to recalibrate the apex tonight too, but I don’t trust that probe one bit.

[bertoni]

I'd get a second opinion from a LFS before doing anything. I tend to trust the new calibration solution more, but I'd check. If the salinity is that high, I'd lower it over a period of a week or two.

[Playapixie]

Results of multiple calibration attempts:
My tank calibrated against new fluid: 40 PPT
Calibrated against the old fluid: 35
Calibrated against distilled water: 38

I also recalibrated the Apex with new conductivity calibration fluid, and for a brief period, it read 40 when it was in my display. Moved it to the sump and it’s down to 36.5, but that may be from top-off water not fully diffusing through the whole system yet. Or it could be bubbles. I don’t trust that probe; too touchy.

It would sure be nice if I could trust any one of these calibrations... *sigh*

I ordered another new bottle of calibration fluid (different brand) which should arrive wednesday, so I guess we’ll see what that says. Meanwhile, slowly brining the tank salinity down a bit...

[homer1475]

And this is why I threw out my apex probe(never trusted it as it always read off from several calibrated refractometers), and bought a milwaukee digital. You never calibrate it per say, what you do is zero it out, then measure against a known solution. If your known solution doesn't come out, you zero the scale out again.

Also I find having a number to read is easier then trying to figure out if that fuzzy line is at 35 or is it 36 PPT?

[EMeyer]

Make sure you are using the correct calibration fluids. The calibration fluids needed for a conductivity meter are DIFFERENT than those used for a refractometer.

[bertoni]

I agree that you need to have a solution suitable for a conductivity probe. This article might help, too:

http://reefkeeping.com/issues/2004-06/rhf/index.htm

[Playapixie]

Yes, the apex probe was calibrated with probe calibration fluid. The refractometer was calibrated with refractometer fluid (two different bottles of refractometer fluid, actually, and I also tried with distilled water.)

I’ve already given up on the apex probe ever being a useful too (not even for trending, changes are basically always bubbles...) I believe it is calibrated, but it’s too touchy to bubbles, electrical current, other equipment, etc, to be useful.

But it’s frustrating not trusting that the refractometer is calibrated. I ordered another bottle of calibration fluid; arriving tomorrow. Hopefully it’ll agree with one of the others, and I’ll be able to start to remedy the situation tomorrow.


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[bertoni]

It's a bit of a mess. Hobbyist testing equipment has significant limits and error issues.

[Playapixie]

It was my old Refractometer calibration fluid that was off. My tank really was 40. Brought it down to 35 over several days. Some clove polyps are still kind of mad but recovering, and one rock flower anemone kind of melted (It had been mad for a while.) Everything else looks great though. Weirdly, nothing actually seemed to particularly mind being at 40, but the swing obviously wasn’t good.

Recalibrated the Alex probe and it now agrees with the refractometer too, but I still don’t trust that probe.


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[Phixman]

Don't worry about what the apex says. Too many things affect the salinity probe. To be honest, I only keep it around in case something goes really bad, like the ATO tops off all the water available or if the ATO container is out of fresh water. My refractometer reads 1.025 and my apex is reading 37ppm

[bertoni]

40 ppt is rather high. I guess we should be recommending that people buy a new calibration solution fairly regularly.

[Joe0813]

guess ive been fairly lucky, my apex salinity probe is dead on