Milwaukee MA887 Digital Salinity Refractometer

The Milwaukee MA887 is a digital refractometer made for one job: measuring the salinity of natural or mixed seawater in saltwater aquariums and reef tanks. Instead of squinting through an eyepiece at a blue line, you put a few drops of tank water in the sample well, press a button, and read the number on the display.

Three ways to read salinity

The meter can show its result in practical salinity units (PSU), parts per thousand (ppt) or specific gravity (S.G. 20/20). That’s handy because salt mix instructions, forum advice and older reef books don’t all use the same unit. Pick the one you’re used to and stick with it, so your log stays consistent from week to week.

Why digital helps

• No line to interpret. Two people reading an optical refractometer can disagree. A digital number removes that guesswork.
• Temperature compensation. Readings are automatically corrected for temperature, so a sample that’s a bit warm or cool doesn’t throw the result off.
• Fast results. Milwaukee lists a response time of about 1.5 seconds.

Range and resolution

The listing gives a range of 0 to 50 PSU with 1 PSU resolution and an accuracy of plus or minus 2 PSU. That’s fine for spotting drift from evaporation or a mistake in a batch of new saltwater. If you want finer steps for a sensitive coral system, cross-check now and then with a fresh calibration standard.

Keeping it accurate

The prism is sealed flint glass set in a stainless steel well. Wipe it with a soft cloth after each sample so salt crust doesn’t build up. Zero the meter with distilled or RO water as the manual describes, and check it against a known standard from time to time. Topping off with fresh water from an auto top-off, such as the XP Aqua Duetto, keeps salinity steadier between checks.

Who should look elsewhere

Freshwater keepers don’t need it. And if you’d rather not depend on a battery-powered meter, a basic optical refractometer costs less and needs no power, though it’s harder to read precisely.