Salinity Refractometer

[garry_boyd3]

Just to finish off the comedy show of last night (I would like to point out I was not drinking, but maybe I should of). I measure 960ml of RO water, heated it to 20 degrees, added two table spoons of salt.... Checked with neat RO water that the Refractormetre was on zero, & the reading I got from it was 1.022, 0.04 off. That would make my salt in my tank 1.030 whic would most prob kill everything, so I think I did it wrong again. At that point I lost the will to live, added more salt water to the stuff while crying into it & decided to go to bed....

Today I am going to try to balance a few millions pound so I may just decide to go home ill....

 

[rabbut]

Considering your refractometer is a hobby level one, that reading and error is near enough correct. With it being hobby grade, prism defects can easily lead to that size of error Mind you, my dad reckons lab grade refractometers are not much better than hobby level ones...

 

[TigerIssey]

Checked with neat RO water that the Refractormetre was on zero, & the reading I got from it was 1.022, 0.04 off. That would make my salt in my tank 1.030 whic would most prob kill everything, so I think I did it wrong again. At that point I lost the will to live, added more salt water to the stuff while crying into it & decided to go to bed....

Wait for the mag result. I cannot see it being that high, when mine was that high due to the Red Sea Max Hydrometer, my Mag was sky high. As was Calcium incidentally.

Take a few deep breaths and try again tonight.

 

[hwoarangtag]

I recently bought a refractometer myself and i am puzzled on how calibrate it.

I think the easiest way is calibrate it with RO water to 0. Then bring it to your LFS and test their tank water that contains corals - preferably their show tank(chances are, their salt level is correct) and remember that reading forever. Then adjust your tank salinity with the LFS' show tank.

 

[garry_boyd3]

Right It been tested separately, so at least I can laugh at last night....

 

[rabbut]

Erm, livestock displays are usually way off. Almost all LFS's are busy to a point where weekly top-up's only occur, so their water may be well off. Also, their salt RO they sell isn't always mixed to the same salinity. You cannot practically use an ATU in a sales tank either, as your salinity would drop at each sale... I'll take four local marine dealerships in my area as examples;

Interfish - upto 4ppt either way of their target
Waterscapes - upto 8ppt lower than their target
Paws for Though - upto 3ppt above their target
Cascade - upto 1ppt either way of their target

As you can see, only one shop has salinity's even close to what they say at each visit I've made. I should point out though, that these are just readings I've taken from my own refractometer after stock purchase, so I may have caught them on off days/weeks e.t.c with my more extream values, and they may not be "typical" of that individual shop...

To get an accurate calibration using an LFS, ask when they last calibrated their refractometer, and how. If it was inside the last month, with a proper (i.e. not home made) calibration fluid within the range you test for a marine tank, get them to test the salinity of a sample of water on said refractometer and tell you the reading. Test the same sample on yours at home and adjust. Then, take the same sample to two or three other dealerships to check the firsts calibration. Also, check they have correctly calibrated their test gear recently. If they are close, but each slightly different, tank and average and calibrate to that. If one is way off the others, dis-regard it. If they are all the same, great, you can be fairly sure of your calibration

All the best
Rabbut

 

[garry_boyd3]

In other words, we can do what we can to be as close as possible & hope for the best then..... However I have found on the sight you sent me for suppliments Calibation fluid. Its only £5 so I thought I wuld give it a go. It says on the wesite "This is also a great way to calibrate Refractometers as this standard solution has the same refractive index as salt water at 53 mS." So worth ago..

 

[AK77]

So basically.... 18g of salt in a 500ml coke bottle with RO water. Shaken, but not stirred, will give a SG of 35PPT?

 

[jtnova13]

why is it bad to just use RO/DI water and set it at 0? Because you don't know if the SG of your water is really 1.000?

 

[AK77]

why is it bad to just use RO/DI water and set it at 0? Because you don't know if the SG of your water is really 1.000?

Yeah. If the RO/DI water isn't pure then there may already be dissolved salts in the water which will make the calibration inaccurate. I suppose though, if you are adding salt to RO water that isn't pure, then its going to throw the reading out too. I've got a 6 stage RO machine and I havent changed the filters in that for well over a year. The TDS meter is still reading 0 on the output, so I'm fairly confident that the RO is sufficiently pure to add the salt into.

Its quite handy actually, as the waste from my RO goes into a rainwater butt. In there are 4 goldfish. They get dechlorinated filtered water to swim in and in return they eat all the mosquito larvae lol.

I also picked up a very good little "Weigh Max" electronic scale from eBay. It was £10 with the shipping. When I got it the first time and was playing with it, I couldn't work out why the ###### thing wouldn't zero itself. The reading kept fluctuating. I thought to myself "Meh.... what a pile of cr#p!!" Then I realised that it was due to air pressure from the fan 2m away, that the scale was picking up lol. Very sensitve!! Its a great investment as it makes for accurate dosing of 0.1g

Cheers,

AK

 

[jtnova13]

my TDS reads 0 and I've put about 130 gallons through it. I used it to calibrate my refractometer to 1.000. I don't see why you need to make a salt solution if your RO/DI is pure.

 

[AK77]

my TDS reads 0 and I've put about 130 gallons through it. I used it to calibrate my refractometer to 1.000. I don't see why you need to make a salt solution if your RO/DI is pure.

I seem to remember Skifletch giving a detailed explanation on this many moons ago. If I remember rightly ( and don't quote me on this because I'm getting old and crusty and have the memory of a goldfish ), its to do with the ranges that different refractometers measure. Having a known SG to calibrate to inside the range that the refractometer is designed to measure, is much more accurate, as the SG of pure water might fall outside the range..... or something like that. Where is WikiSKIdia when you need him??

By far the most accurate way to calibrate the refractometer, is with the solutions that you can purchase, where the SG is exact.

 

[jtnova13]

By far the most accurate way to calibrate the refractometer, is with the solutions that you can purchase, where the SG is exact.

this makes sense.