Refractometer calibrations, salinity issues on SPS, and raising salinity

[Los]

I've been having some die off at the base of some of my acros and only on acros. I figured it was high phosphate (Hanna test kit on the way), but added GFO in the meantime. The recession appears to have either slowed down or stopped. In the meantime, I double checked all my parameters:

tank: 360 main and another 100 in the sump
temp: 76-80 +/- 2 degrees, depending on which thermometer
Alk: 10 dkh
Mag: 1300 - 1350
Calcium: need to check; test kit arriving soon.
Salinity: I thought it was 1.026 per my refractometer, but actually 1.021 as confirmed first with a cheap swing arm and then a floating type hydrometer I just bought.
Ammonia and Nitrites: unmeasurable
Nitrate: approx. 5 ppm, but hard to tell exactly

A few questions I'd love some experienced advice on:

1) I thought I was being smart calibrating my refractometer by taking fresh RODI water and setting my refractometer to 0. Does that not work and if not, any idea why?
2) Because two mechanical devices (swing arm and floating type) both say 1.021, is that possibly a cause of my recession at the base of the acros? All the other corals look fine and I don't have any fish in the tank.
3) I'm worried that if I've adjusted my alk and Magnesium to be high enough (via calcium reactor and lots of magnesium flakes) at 1.021, when I add more salt water to the top off and gradually raise the salinity that way, I'm going to raise both of those by roughly 25%. Is that likely to be a problem and how long should I take to make the adjustment. I was thinking of doing it gradually over a week.

I love being able to get plugged into experts by punching a few keys! Thanks in advance.

Los

[cwegescheide]

Randy Holmes Farley has a home recipie for making calibration fluid of 1.026 using table salt and a 2 liter bottle. My refracto was way off btw as I found out thanks to Randys calibration formula. I whipped up a batch and it was perfect. I even went so far as to take my refractometer to the local aquarium (I live within walking distance so what the heck) and it was spot on. If I were you I'd go to the Reef Chemistry forum and check it out.

Phosphates are more often than not the culprit to SPS woes but I'd also make sure your refracto is correct.

Good luck,
Chris

[palawan]

Buy yourself a refractormeter and don't rely on those plastic hydrometers. I have a refractometer and I made and used the homemade calibration solution of Randy H Farley but for some reason their was a variance somewhere. So I went and bought a pinpoint salinity monitor calibration fluid for accuracy. I also bought a glass hydrometer for backup. I've had swings in salinity and DKH and believe me SPS don't like swings in parameters. I had some that started to RTN at the lower portion. Just remember that you need recover parameters slowly and not abruptly.

[Los]

Thanks Chris and Palawan. I actually have two refractometers, it's just they've both been (wrongly, apparently) calibrated using RODI water. I agree, they are the way to go. Chris, I'll go with your suggestion on the Randy formula. Thanks for the pointer. Does anyone know why calibrating it to zero using RODI water doesn't work. Weird.

[dots]

It will be close enough for the time being to do it that way.



Double check you have the correct type of refractometer, because all are not for marine use.

Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/index.php

Temperature Corrections for Hydrometers
http://www.reefkeeping.com/issues/2004-07/rhf/index.php

Specific Gravity Measurement
http://www.advancedaquarist.com/2002/1/chemistry

Reef Aquarium Water Parameters (a summary general article)
http://www.reefkeeping.com/issues/2004-05/rhf/index.php

Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.htm

or buy your own, just use lab standards to not contaminate it, and it should last for a very long time.

American Marine Pinpoint Salinity Calibration Fluid
http://www.marinedepot.com/ps_ViewIt...s~vendor~.html

[stunreefer]

Hey Los,

Grab yourself some of the 35PPT Saliny Calibration Solution, and calibrate the refractometer to 35PPT. Its cheap and most places carry it.

The refractometers we use have a very broad scale and aren't the "best/most accurate" testing equipment out there. By calibrating them to 35PPT, we are calibrating them into a range we will most commonly use in the reef hobby. By calibrating with RO/DI, we are calibrating the refractometer to its lowest ranges.

Hope this solves your issues man, I ran into the same thing before.

[msch1999]

Originally posted by stunreefer
Hey Los,

Grab yourself some of the 35PPT Saliny Calibration Solution, and calibrate the refractometer to 35PPT. Its cheap and most places carry it.

The refractometers we use have a very broad scale and aren't the "best/most accurate" testing equipment out there. By calibrating them to 35PPT, we are calibrating them into a range we will most commonly use in the reef hobby. By calibrating with RO/DI, we are calibrating the refractometer to its lowest ranges.

Hope this solves your issues man, I ran into the same thing before.

+1 I use the same solution

[Reefer07]

I am actually having a similar issue. Here is the post I just put up before coming here:
Today I got a Milwaukee refractometer. I calibrated it by following the directions. I measured my tank at 1.030!!
Now I have always measured with a hydrometer but I have checked it with a friends refractometer. Now I have no problems in my tank or at least nothing appears to look bad. I have a 29g mixed reef with some SPS that are thriving.
My question is what are the chances of my SG being really 1.030? Whatever they are it's always been constant.
On the hydrometer I always mixed my salt to 1.025 and I have always measure it from my tank as 1.025.

I am thinking I calibrated it wrong some how. Is there any way the refractometer could be damaged or as long as it's calibrated properly it works?

The only thing that seems strange is about the temperature having to be 65 degrees or something.....

[Los]

Thanks for the recommended solutions and links. Dots, it took me a second to get your signature line: "Putting round blocks in square holes everyday." Absolutely brilliant! Frag plugs in a eggcrate, for the those who want to save a second of thinking. I love it.

Austin, I'm going to test and calibrate against 35ppt solution today. I'm very curious to see what it really is.

Reefer07, I know little, but one thing to watch out for is if your refractometer has ATC (Automatic Temperature Compensation). If you don't, then temperature does become part of the equation. You should be able to look up a chart online to convert your reading at your temperature to what it actually is on your refractometer if it isn't ATC. I think the advice I got here about calibrating it at 35ppt is good and something I at least intend to follow. I'm glad to see this thread is good for someone else too.

Thanks again guys!

[Reefer07]

Damit, ATC is something I wish I looked into and spent the extra bucks. I don't know if mine has ATC but I'm going to say it doesn't.
Thanks Los and good luck.

Edit: This really ****es me off. I got just about the only refract without ATC and some of them with ATC were even cheaper!