How accurate are refractometers?,

[Miller535]

Swirling is quite effective...maybe next time you use the calibration fluid try one test before you shake, then one after shaking, see the results.

I do mix the quantity again I need for the water change when bring it to temp but when I've tested the standing salt water it was the same salinity.

I'll give it a try.

 

[Anchor]

Swirling is quite effective...maybe next time you use the calibration fluid try one test before you shake, then one after shaking, see the results.

I do mix the quantity again I need for the water change when bring it to temp but when I've tested the standing salt water it was the same salinity.

Try and answer some of the questions brought up..

At the level of salt in the cal fluid, you shouldn't get salt to fall out of solution. Shaking will create bubbles. Any lab tool with a sight glass.. AKA Hanna ALK/PHOS/CAL, refractometers etc., will be effected by bubbles/micro bubbles anywhere from slightly to a lot .... Hanna checkers = No shaking - even the instructions say to invert.

The number of drops of cal fluid onto the refractometer shouldn't make any difference to the reading you get either. the weight you press against the LED cap or cover should equalize the film between that and the sight glass. It is not like this is a really viscous liquid.

Turning on your pump in your mixing barrel should also not effecct what you get though there may be some evidence of weight separation in the water with lighter, less salty water at the top.. so turning on the pump should at least not hurt. Could experiment there easily.. Salt, once dissolved, should stay equal within the water. I cant see any noticeable stratification of the water column using the tools we have to measure it with..

As an added note.. Keeping the inside of a cuvette clean is a huge deal.. If you can get small Non-wire wound brushes meaning plastic, small enough, Use them inside your cuvettes every couple of uses. I just broke my plastic one but can provide a pic of a metal wire one if you want more clarification. Use RODI water too. And nver store an old test in a cuvette. If not cleaned it will show you some disturbing results.. Especially Phosphate. For instance, say .15 phos and 3 days later 0.. because the cuvette was dirty and a film formed from the previous test.