Instant Ocean SeaTest Hydrometer
$ 4.77
This is the second hydrometer of this model that I’ve owned (they do get erratic over time even when rinsed and stored with RO water, I think because the pivot point wears and also gets precipitate on it). The previous one read one point high, while this one is accurate.Any plastic swing-arm hydrometer will have issues with air bubbles sticking to the arm when the hydrometer is new — that’s often why people have issues with these things. I soak mine in salt water for about three days, rinsing with RO each day then refilling. That seems to remove the film on the plastic that attracts the air bubbles.Swing arm hydrometers also should be checked for accuracy. I calibrate them against a (properly calibrated) refractometer. Once I determine how high or low the hydrometer reads, I make a note of that (I use a permanent marker to note on the back of the hydrometer, e.g. “This hydrometer reads 1 ppt high”). Then I have an easy to use, accurate device to do routine checks of salinity (well, actually specific gravity). The more tedious-to-use refractometer is used for periodic sanity checks.
