Salinity... got a refractometer and it's a bit high.

[sikemd]

I've been using a floating glass hydrometer for the last few months for my salinity/temp measurements, but a few days ago I broke it cleaning it. So I bought a new one and a refractometer.

The new glass hydrometer reads a bit less than my old one. The old one was reading dead on, 1.024 this one is reading less, 1.020. So I checked with the new refractometer and it is reading ~1.030 which is certainly higher than optimal. I'm not sure how bad 1.030 is in terms of detrimental effects to the tank but I want it in the optimal zone.

So first off, how serious of an issue is having 1.030 SG? I'm going to guess it's probably been up and down and not where I had thought it was since day one (tank is 6 months old). The tank has and is doing pretty well but I'm guessing it could be at least a little healthier and perhaps a lot healthier if the salinity was proper.

Second, what the time frame should I target for dropping to 1.024 from 1.030? Can I try to do it all in one water change (preferably 5-10G)? My guess is that it wouldn't be a big deal trying to do it all in one change considering it will take a good while for the current water and new water to fully mix (as long as the change doesn't go too far off). It's a 90G bow front with about 10-15G sump tank. Any suggestions on approximate amount of water I should change and an estimate of salt content level I should put in the replacement water?

Or... am I just going to have to play around with it until I get it right? I'm guessing this is probably what I'll end up having to do.

 

[ReeferMaddness843]

Following. Getting my refractometer delivered today so we shall see the damage on my own as well. Smh. Hope all goes well and best wishes on lowering slowly.

 

[scardall]

https://www.hamzasreef.com/Contents/Calculators/TargetSalinity.php

 

[ReeferMaddness843]

Awesome tool. Thanks from me as well

 

[Rybren]

That's a pretty wide spread. Did you calibrate your refractometer? If you did, did you use calibration fluid?

If you didn't calibrate or if you calibrated with something other than a proper calibration fluid, then I wouldn't trust the readings.

 

[ReeferMaddness843]

Whew! 1.027 here with refractometer after a year of swing arm testing. Gonna drop that .001 and have it exactly where I need it. Yay

 

[sikemd]

I calibrated it but I didn't use any special fluid. The instructions said just to use distilled water.

 

[sikemd]

That's a pretty wide spread.

I was going to make the change in one single 20gallon WC based on that calculator. Is this a bad idea?

 

[Waterjockey]

I was going to make the change in one single 20gallon WC based on that calculator. Is this a bad idea?

I would just remove a jug of saltwater each day and replace it with rodi. As the saying goes, nothing good happens quickly in a reef tank. The gradual change will be better for your system as a whole in my opinion

 

[sikemd]

I would just remove a jug of saltwater each day and replace it with rodi. As the saying goes, nothing good happens quickly in a reef tank. The gradual change will be better for your system as a whole in my opinion

I like that idea. Easy, slow and safe.

 

[morpheas]

Depending on the quality of the refractometer calibrating at the 0 point (with the RODI water) and then measure, could easily take you .001-.003 off at the region of interest (1.025). I would suggest you don't make any changes until your refractometer is correctly calibrated with sea water reference solution. You can get some for $7 from BRS and other vendors.

 

[sikemd]

I think I'm going to do that. I'm reading a lot about inconsistency with 0 calibration point. Calibrating with solution, do you calibrate refractometer at 1.025 and shoot for 1.025 when testing?

 

[miyags]

Calibration fluid is 35 ppt. calibrate to that. You can lower Salinity fairly quick. Raising it is when you take it slow.

 

[sikemd]

So... I ordered Calibration fluid, but it will not be in until tomorrow.

However, per this post (http://www.nano-reef.com/topic/347325-will-rodi-water-work-to-calibrate-a-refractometer/) someone suggests a calculated mixture of salt/water to make 1.026SG solution.

1.3394 Refractive Index, Refractometer calibration fluid:

Mix 3.65 grams Morton's Iodized Salt (NaCl) and 96.35 ml (or grams) RODI to make a ~1.026 S.G. calibration standard.

So I tried it, weighed with a digital scale to exact measurements, and refractometer was dead on 1.026. I'm going to say I trust that result and concluded that my salinity was actually 1.030. I did some WC w/ measurements from the calculator and brought salinity down to 1.026.

You can lower Salinity fairly quick. Raising it is when you take it slow.

Thanks for that!

So in my case (if correct) RODI worked perfect for calibration at 0% and read accurate at the target range. At least I think, I will post results of calibration fluid when it comes in, but I am nearly certain it's dead accurate.

This is the refractometer I bought ($21):

https://smile.amazon.com/gp/product/B005ES6MOQ/

I did a lot of experimenting with different waters/solutions over a 2 hour period (while experimenting with hannah phosphate checker). Fun stuff, but also confusing.

I've read different refractometers can act differently so I can't guarantee the same results for everyone, but this is just my experience for what it counts.

 

[Scott.h]

Definitely don't use distilled water for calibration. I haven't used my bobber in years. I have a conductivity probe that was jumping around recently, so I pulled my bobber out. That read 1022, my calibrated refractometer was 1025, and my apex calibrated conductivity probe was 1029. I trust the refractometer. At 1029 things start to suffocate. Snails will die.

 

[truepercs]

Pay attention to water temperature when using refractometer.

 

[jsker]

https://www.hamzasreef.com/Contents/Calculators/TargetSalinity.php

I used the same sites conductivity calculator. Thank you I did not know this one was in there also. I guess I need to do some exploring.

 

[truepercs]

I try to calibrate the refractometer with pure water that is at a temperature that is the same as the tank. If water temp is much different I found that readings are inconstant. At least that is what I find with mine.

 

[DLHDesign]

For the ATC (Auto-Temp Correction), be sure to let the sample sit for ~45 seconds before reading it. Here's my process:
1) Dip a dropper well below the surface (surface water can potentially have different salinity than the rest of your tank) and suck up as much water as possible
2) Repeat (1) above several times (goal is to flush out any old water/residue with the water to be measured)
3) Hold the sight glass level (tilt the refractometer) and slowly add enough water from the dropper for the water to bead up on the surface of the glass
4) Close the lid of the glass, making sure that there are no bubbles trapped beneath (if there are, add more water)
5) Let the refractometer rest for 45sec
6) Take a reading, holding the sight glass directly at a source of light
7) Clean off the sight glass with a towel and repeat 3-6 above one more time in order to ensure a true reading

If the line in the glass isn't clean and distinct, then you likely have either bubbles or debris trapped on the sight glass; best option is to clean it off and try again.


The idea of the calibration fluid (versus RODI water) is that refractometers have more of a variance the further away from the calibration point that you get. Think of it like a magnifying glass - if you focus the middle of the lens just perfect, the edges are still just a little bit out of focus. Same with the prism in use in the refractometer. When you calibrate to 0 (RODI water), that results in the device being "perfectly" able to read 0, but the further you get away from 0, the less accurate the reading will be. Calibration solutions at 35ppt (1.0264 SG @ 77F) are right in the area of natural seawater and are close to what most people are looking for in their home aquarium. Calibrating to that will ensure that you get the most accurate reading possible.
TL;DR - Calibrating with RODI is better than no calibration at all, but 35ppt solution is better.