Need help with my at refractormeter

Fishyj · Dec 10, 2015

Hi all, I have been having a terrible time calibrating my refractormeter. I always have calibrated with 35 ppt solution. I ran out of this solution and I ordered more online. After calibrating this I did my 10 gallon water change and that's when my problem started. The corals did not like the water change. Some how the calibration is off. I purchased an instant ocean hydrometer just to compare. I have a reading of 35ppt on my tank. I found the instructions and mine says to calibrate with distilled water to zero. If I do this my test solution is now reading 1.030. My tank water reads 1.028 and my hydrometer reads 1.028. Could my test solution be bad. Looking for advise here.

Downbeach · Dec 10, 2015

You should be using a fluid with the same refractive index as the sample you'll be testing, so the 35ppt solution is what you need; not RO/DI or distilled water. How old was the solution you had been using? Are you sure you ordered a solution made for use with a refractometer and not just a conductivity probe? How big is your system and how much of a WC did you do? Was your WC water heated (if necessary)?

Randy Holmes-Farley · Dec 10, 2015

There may be many possible issues here, but a sg of 1.028 should not usually harm corals, and a single water change wouldn't push it up very high. Even if the new water had a sg of 1.0300 and the tank was at 1.0260, a 10% water change will only boost the sg to 1.0264.

FWIW, corals thrive in the Red Sea at an average specific gravity of about 1.030, but lowering it slowly is a fine plan if it really is high. I try to target a level reflective of 35 ppt seawater, which is about sg = 1.0264

The test solution may certainly have evaporated (and concentrated), which could cause the tank salinity to rise to match it, and may be why the standard itself reads that high when calibrated with distilled water.

In general, calibrating with RO/DI or distilled water will give a different value on most refractometers than calibrating with a 35 ppt standard. But it wouldn't be off that much.

What brand standard and what did you set the refractometer to when you calibrated it (before the recent issues)? Most that I know of should read 35 ppt or sg = 1.0264, but you usually can't independently elect both, so pick one of the two scales (if yours has two, ppt and sg) and use only that one that you calibrated.

Fishyj · Dec 10, 2015

Should have been a little more clear. I have a bc 29 tank and I do a 10 gallon water change. When I calibrated my refractormeter, I did use a solution that came with it. I did order a solution from pet solutions which buckeyehydro makes. If I calibrate with the solution my tank water reads 1.035 afterwards. If I follow the instructions that came with the refractormeter and use distilled water then my tank reads 1.028 which is the same as my hydrometer. I have taken out some water and replace with ro water and my corals have started opening up.

Randy Holmes-Farley · Dec 10, 2015

I'm confused.

You just said the tank water reads a lot higher than the standard does on your refractometer? Is that the new standard, and when you made the water change water, you used it for calibration, and then used that calibrated refractometer to measure the water for the water change?

My quandry is I don't understand how you might make a water change batch so high (high enough to get the tank to 1.035) when the standard itself is only reading 1.030. Presumably you were not intentionally making a batch of water a lot higher in specific gravity than the standard???

Maybe you had a calibration mistake when making the new batch of salt water?

Downbeach · Dec 10, 2015

In either case your SG seems to be a bit too high. I would have more faith using the 35ppt solution.

Randy Holmes-Farley · Dec 10, 2015

Downbeach said:
In either case your SG seems to be a bit too high.

I agree, I'd look to lower it.

Fishyj · Dec 10, 2015

I did not calibrate before the water change. I normally calibrate it once every couple of months. The only reason I started checking it was the way the corals responded to the last water change. I mix between 5 and 10 gallons a week for my water change. Should I order a different test solution? I will be taking in a water sample to get tested to see where I am at.

Randy Holmes-Farley · Dec 10, 2015

I'd get or make a new standard just to be sure. And be sure it is a name brand of some sort (like Pinpoint) if you do not make it yourself.

Fishyj · Dec 10, 2015

Thanks for the help.

Randy Holmes-Farley · Dec 10, 2015

Your welcome.

Let's us know how things turn out.

Fishyj · Dec 10, 2015

Just an update. The solution I had was bad, I purchased some from my lfs and was able to calibrate. My tank was at a reading of 1.031. I have dropped it down to 1.027 and everything is responding well. Once again thanks for your help.