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Coral Vue Hydros

need to vent a little....refractometer swing


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I just need to vent a little...how often does this happen to you...


So I was just about to change my water, and I spot checked my tank water with the refractometer. Calibrate with R/O and the reading came out at 1.025 just as I expected. :D


So I head downstairs to do a check on the replacement water, which I get from a LFS and the salinity varies. The water has been heated and been mixing with a power head since yesterday in preparation of today. It checks in at 1.021.


ok, no big deal- I expected this- the LFS usually runs 1.021-1.023. As usual, I add salt to bring it to 1.025 over 15 minutes so I don't overshoot. Been there, done that. So I let the replacement water mix for a while longer and re-test it and it comes out at 1.025.


Everything's good to go...NOT


for some silly reason I re-check the fish tanks water, and now it reads...wait for it....1.021. I'm like ????...how in the heck....???? ok, re-recalibrate with r/o.....check tank water again....1.021......WTH!


I know this cant be right, so i adjust the refractometer to read 1.025 (I know the tank is 1.025) and re-re-retest with R/O (now expecting to see it sit a little high on the baseline)....and get a 0. :angry:


back downstairs I go....

Check the replacement water....1.029 :angry:


ARGH!!! So frustrated.


So I break out the swing arm....replacement water = 1.029. :angry:

Test upstairs tank...=1.025. :D





I know that these refractometers are touchy...but seriously, within 15 minutes this thing has given me different readings on the same water 2 times.


So now I'm diluting the new water back down to 1.025...or so I think.

:angry: :angry: :angry: :angry:

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Do you have big temp swings between upstairs and downstairs? I purposefully keep my refractometer upstairs in the kitchen, where the temp is fairly constant, and only measure from there. So I'll get my pipette, pull the water from the downstairs salt bucket, then measure it in the kitchen. I calibrate and do all measurements in the same exact spot in the kitchen so I hardly ever need to re-calibrate it. I've noticed that when the temp fluctuates in the kitchen as the seasons change I have to recalibrate it then. But otherwise, keeping that factor constant re-calibration is almost never necessary.


(Edited to add:) Oops didn't read that you were calibrating with R/O - yes, you need to use a calibration solution instead as paneubert said. It's the best way to minimize any problems with your refractometer readings (apart from what I mentioned above re: ambient temp swings).

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I feel your pain. Something to consider might be buying some calibration solution just to be sure. Calibrating with RO/DI is dangerous since the error curve is a lot higher when trying to calibrate to zero as opposed to 1.025 or something close to it. Technically you are supposed to calibrate to something close to what you plan to measure due to a lower margin of error.

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Damn you have it bad, I just have my salt already measured and mix with the water. It comes out to a perfect 1.025 all the time. No need to bust out the refracometer.

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I knew these things were temperature sensitive, but I hadn't thought that it was this sensitive. I just took a digital thermometer to the bathroom where the water is, and it was 3 degrees warmer than upstairs. I had never noticed that before.


I will not rule out user error. I know I make my fair share of mistakes....


I agree with the calibration fluid suggestion, I have thought of buying some before but never really had the urge to pull the trigger. I also agree that taking the measurements in the same place is also a very good idea. Usually I am in the same room, but lately the wife has not been fond of having a 5 gallon water jug in the kitchen overnight heating/mixing, so I have been moved downstairs to the basement for my water heating/mixing duties.


I guess now I know that I just need to move my gear upstairs when its time to change the water...


lesson learned. :rolleyes:



question for neet: how do you premeasure the salt for the water? what kind of scale would be used? I would mix 5 gallons at a time... would a digital food measuring scale be accurate enough for that little amount of salt?

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question for neet: how do you premeasure the salt for the water? what kind of scale would be used? I would mix 5 gallons at a time... would a digital food measuring scale be accurate enough for that little amount of salt?


Buy one of these:




I believe 1/2 cup of salt = 1 gallon of 1.025 salt water (Just double check)

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that all depends on the type of salt you use! Most bags will tell you about x many cups to x many gallons. My salt is 7 cups for 15 gallons of water, for example.

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I've noticed that my refractometer is really sensitive to temp, and I'm in florida. :D


The routine I have now is to use the calibration fluid (a must!), then check the tank, then check the mixed water. For the amount of money I have wasted on other stuff, the calibration fluid seems like a small price to pay for my peace of mind.

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Name calling and insults are completely unnecessary and will not be tolerated in the general forums and especially the Beginner Forum. Thank you to those whose comments have been positive and helpful.

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