 icenine wrote:
I've never had an issue zeroing using RO and can't imagine why you would. You could even use tap with a reasonably low TDS. Calibrating with tap water that
has a TDS value of 350 ppm introduces only about a 1% error
in salinity, causing readings in saltwater to read a bit low.
So 35 ppt sw (specific gravity = 1.0264) will read to
be about 34.7 ppt, and will show a specific gravity of about
1.0261.
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remember that a refractometer is not really reading the salinity. It is telling you the level of refraction of the elements in the water that you are measuring. So while RO water is pretty clean and should have a low TDS it is still not "pure". Distilled water has the fewest number of contaminants in it for easily available water. While RO water won't throw you off "a lot", as I mentioned before, it throws my meter of a noticeable amount.
I guess you could relate it to gasoline. most cars only need regular grade gasoline, but some cars need mid grade gasoline and if you put regular in them they still run but not as well. They obviously don't stop working but if you're using a refractomoter I think the point is to have it as accurate as possible, right? Otherwise you could just use your old Instant Ocean salinity guage. :)
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