Refractometer Calibration: the Myth and Risks of using RO/DI

[Pufferpunk]

Since this could be good for several of the forums here, I'm just posting it in the Gen Disc Forum.

http://blog.captive-aquatics.com/captiv ... -rodi.html

[jus85411]

interesting... now i know when i get a refractometer to just get the calibration liquid also. thank you for that find!

[JRC3]

So could you mix 1 part solution to 5 parts of RO/DI water to calibrate your refractometer for BW of .005? Or if you calibrated it with full strength solution at .030 would the refractometer still be accurate down to .005?

[Pufferpunk]

The calibration solution is to calibrate the refractometer, period. At that point, it will be good for all SGs.

[geronimo69]

That was a good read PP...

My suggestion (and what I do/have done)... is bring your refractometer to your LFS (in my case I brought it to 3 different ones) and have them test it in comparison to their own refracto/hydrometer. I've never had any problems.

[Pufferpunk]

Who says they use calibration solution? I'll bet most use RO water to calibrate. Ask!

[RTR]

Please, please remember that RO is not, repeat not, DI or RODI.

The output product of RO varies enormously with the membrane, the operating pressure and the rejection rate. Purchased DI also can vary quite a bit, but not as much as RO. If you have access to WFI (water for injection), that is a much better standard for zeroing the refractometer. If WFI is not available to you, RODI is the next best bet. RODI and WFI cannot be stored in glass or exposed to the air. Capped inert plastics are proper storage containers and the smallest convenient contairers are the best. Multiple repeat uses of an open bottle can in itself lead to error - this is the reason for selecting smallish bottles to be more practical for disposable fairly frequently.

All purified water products are not, repeat not, interchangeable. If you zero the refractometer with RO alone, all bets are off. You will have no more than a guess at what your specific gravity is.

Refractometers are precision instruments. Improper calibration makes them give meaningless numbers.

HTH

[geronimo69]

Who says they use calibration solution? I'll bet most use RO water to calibrate. Ask!

This could be.. But they've had established tanks for 10+ years ( the displays, they don't change often ). There are all types of sensitive corals, so my assumption, is that they have their specific gravity set to the proper level.

But as usual, I agree. Easy to ask!!!


On another note... I use distilled water for my reef. Would this work to calibrate? RTR?? I have not used it, but am curious to know.

[RTR]

If it is fresh HDPE or comparable stored Cati/Ani column DI, it should be fine for zeroing the refractometer. Commercial distilled water from a boiler and condenser setup depends too much on the equipment operation and upkeep, I would not trust it myself.

DI = de-ionized water. DW = distilled water. They are not the same thing at all.

HTH

[Pufferpunk]

Who knows the condition of the filters for that bottled "distilled" water?

[Dadof4]

I just ran calibration on my refractometer with all the sources mentioned. Distilled water was WAY off (as much as .004), RO/DI was also was off but better (Varied on the source, I got it from the dialysis machine at work and the LFS, .001-.002 off), WFI (I have it at work) was the closest to the manufacturers calibration fluid. I originally calibrated mine with RO/DI then got the calibration fluid a few weeks later.

[RTR]

Dadof 4 - have you tried WFI? You should have access. If fresh it should be the best around for zeroing. It is basically reprocessed RODI, but the last step is the $$$ one. it is what I used for calibration and my cultures in the lab Now I have to use commercial, but it is almost as good as what I generated in-house.

[geronimo69]

Who knows the condition of the filters for that bottled "distilled" water?

Hi PP,

I assume you are referring to the distilled water I speak of. I do not use the "bottled stuff". I have a Dolphyn (I believe that's the brand name) distiller at my house. I distill my own water. The upkeep on the machine is done very well. I clean it a minimum of once a month. I think it is great. It was originally about $2000 to buy/setup, but has been worth every penny.

[Pufferpunk]

I was referring to bottled distilled water at the grocery store.