- Location
- Duluth, Minnesota
you had mentioned that there are only three sea water refractometers available to us. what about the DD H2Ocean natural sea water refractometer?
I gave them all the data for that unit and it was suppsoe to be good thing. However, it has no all panned out right and Stuart may redo it. It was suppose to be a seawater refract but it is not. It lays between a Seawater and a Table salt refract ( which almost all are using). You need to cal it in somethign like PinPoint 53 mS cal solution. This is why if you cal it in RO/DI and check with 53 mS is will be off or if you cal in 53 mS and then test RO/DI it will be off, which you have seen.
it also states that the calibration temp. of the refractometer is 20*C/68*F
You do not really need to, as it is a ATC refract and is good +/- 15 - 20 F from 68 F.
the esv salt mix instruction indicates that their 34 ppt is 1.0256 @77*F, should that still read 34 ppt on the refractometer if the fresh saltwater is 79*F?
Yes.
i have a spare chinese refractometer that i also calibrated at 35 ppt using the pinpoint solution
And that is all you need to do. Put some 53mS on the plate an cal to read 35 and you are good to go but for a narrow range, say 31 - 39 ppt.
should i calibrate that to 36.5?
NO, this is if YOU are making up a table salt solution to use and you are not.
but the conversion chart indicates that at 53mS and 35 ppt, the sg is 1.0259
It is wrong and has been wrong for years. I have told Lou to fix it but he never has. @ 25 C (77F) 35 ppt = 1.0264 = 53,056 uS (53mS) Lou is basing his on Density @ 15 C, 1.0259 and Density is not SG. If he did it right it should read corrected 1.0269, SG not 1.2059 D. If we used his D @ 1.0259 the Salinity 33.7. We do not use 15C anyway but 25 C Std.
right now my tank reads ~36.5 ppt or ~1.0275 on the DD refractometer but the pinpoint monitor reads between 53.5-54.0 mS which is 35.40-35.7 ppt or 1.0262-1.0265 in s.g., the tank temp is ~79.5*F
You are within the accuracy of these units, which is +/- > 1 ppt , 0.001 Sg or 1 mS.
