[mike31154]

I like to think I'm relatively careful with mine, with regard to the bumping & handling biness. It still goes off cal a point or 2 from time to time but I don't sweat it that much. I generally use it when doing water changes to compare the tank water to the new water simply to confirm that the difference is not too much. Water changes are large in my case, about every 21 days so I'm not too keen on shocking the livestock by dumping a bunch of new water with significantly different salinity on them. So, regardless of whether the reading is off (I shoot for 1.025), provided the tank & new water are within 1 point, I go for it.

IMO, it's easy to over think these things. I mean once you have your tank salinity set to the desired value & your top off system is working properly, there really isn't anything other than a water change that will tend to change it. This is why I simply ensure the new water is close to the tank water before I do a change. If I feel ambitious, I'll put a drop of tap water on the refractometer & tweak the adjustment to make it read 0. Other than that, I see the tank virtually every day, so if something's amiss, I investigate. Usually it's not incorrect salinity. After years of running the tank & making up new water in the same container using the same salt, I have a pretty good handle on how many cups I need to mix to get close to 1.025. So should be no reason for the tank salinity to drift more than a point after a water change.

A few years ago I used the refractometer to compare tank water readings with 3 cheap swing arm hydrometers and a floating hydrometer. Salinity showed 1.025 on the refracto. The floater was bang on same as refracto, the swing arm jobs were all off by quite a few points. Rather than turf them in the trash, I put a mark on each of the cheapo swing arm hydrometers to show where 1.025 was according to the refracto. So theoretically I should be able to use the swing arms to confirm whether the refracto has drifted or not. Haven't done that in some time though, so I should probably trash them. Nevertheless, if anyone has a swing arm still kicking around & is concerned about their refracto drifting, they could do the same & use it as a backup. Better yet, invest in a floating hydrometer, they are very accurate, provided you use them at the design temperature, or compensate with a chart.