Instant Ocean Hydrometer

Fill it all the way to the top, tap it to remove any bubbles, take a reading and then repeat to make sure. If you can, get a refractometer - they're MUCH more accurate and easier to use and don't cost much more than a swing-arm hydrometer.

I am using the same one and have actually found it to be accurate. Though not as accurate as a refractometer. You do fill it to the top and tap the bubbles off the needle. I would try using some distilled bottled water to make sure it reads on the zero mark.

definatly get a refractometer, you can find some online for like 40 bucks. the thing is about hydrometers, even if you test them, they do get more and more inaccurate over time because of build up and wear. If you are using a hydrometer, get a refractometer, if you cannot do taht at this moment, then ocne a month wash out the hydrometer with rice vinagar to remove build up.

A little advice for down the road........

I use an Instant ocean salinity tester - A problem i have had with this, when shaking off the bubbles, is the little weight in the tester arm falling off. If this happens to you it is very easy to slide the weight back into the hole with a needle nose tweezer - just thought i would give my experience with this piece of equipment.

If you do a little jig (sweep instead of plunge) you can get a pretty accurate reading with a hydro, that's what I do if I'm in a hurry. However if the reading is out of whack I grab the refract (hey that ryhmes sounds like "if the glove does not fit...."). Anyway....... I use the hydrometer if I pretty much know the salinity of an existing tank and just need to verify I'm still o.k., and use the refract to mix water or on new tanks where any noggin' scratchin comes into play.