Quick summary first and full review below:Positives:Rugged designWaterproof and dust proofBatteries and lanyard includedDifferent measurement optionsCalibration optionInstructions in clear EnglishGives quick, reliable readingsReplaceable sensor (although not readily/cheaply available in UK)Negatives:Screen not very large and not illuminatedInstructions in small printSlightly more complicated than simple TDS meter, due to different measurement unit options (although latter is also a plus)I had previously bought a cheap TDS meter, but decided to get something a bit more reliable, as the electrodes don't last forever, anyway. I use it for plant nutrient solutions, but it would work for any liquid application. It displays as TDS in ppm or ppt (at 2 different conversion rates), mS or micro-siemens. Generally, in hydroponics, what's referred to as EC is measured in mS, or if you multiply that by 10, you get the CF value. In case you don't know (I didn't before): TDS meters measure electrical conductivity (EC) and convert that value to TDS, for which there are different conversion rates. You can look up the conversion rates in tables online. This also provides a temperature reading in C or F and automatically compensates for temperature (which otherwise affects the reading). I've not calibrated it yet, so can't say for sure how accurate it is, but am confident it's more than accurate enough for everyday purposes and readings remain the same for multiple measurements. I looked at the Essentials EC meter (only 1 review, but their ph meter has many good reviews), at a slightly lower price, and providing similar specs, but with this one, you can replace just the sensor, which you can't with the Essentials meter. However, the replacement sensor does not seem to be widely available. After a bit of searching, I found out the part # for the sensor: if you search google for "HM Digital SP-C1", you will get some results. Cheapest I saw was on ebay, sent from US, for about £25 with international tracked delivery. This is more than sturdy enough for everyday use, and has an IP67 rating (dust and waterproof for immersion up to 1 meter, though not hermetically sealed). Instructions are in clear English, easy to understand, but the writing is small. It comes in a box with plastic insert, with a ribbon lanyard that fixes to the top and AAA batteries. Measurements stabilise very quickly. The screen is not huge, and displays multiple values, but is easy enough to read with normal eye sight in good light. There's no backlight, which would have been a nice feature for poor lighting situations. Overall, am pleased with it for the price, and would recommend.

Es practico y preciso me agrada que es a prueba de salpicaduras y la calidad del equipo es buena

My aquarium runs on 7GH and 2KH, this meter reads 400+TDS, my cheap ones all read 200-250, there is no way with those parameters im at 400+ TDS with weekly water changes. For that price an absolute junk item, very dissapointed.

I purchased my COM-100 meter well over a year ago, in Feb 2012, and its performance to date has been flawless. I purchased a bottle of the 1000 ppm calibration solution along with the meter. To date every test I've made of the meter's accuracy has been right on the money without a need to adjust calibration, and I'm still on the original batteries. I use this meter primarily for testing the ppm of the ionic colloidal silver I make at least monthly. I also use it for testing the ppm in my home water, hot and cold, and purified water produced by my reverse osmosis machine. The RO machine takes my home water @ 350 ppm and purifies it down to Update: 1 Feb 2014I continue to frequently use this meter for checking TDS/ppm on: faucet water, RO unit water, swimming pool water, rain water, roof runoff water, steam distilled water, and even colloidal silver I've brewed. I also purchased HM's 1000 ppm TDS test solution that I use occasionally to retest the accuracy.. I've never had to recalibrate it. This is a great test instrument that appears to be quite tough and highly accurate. I've had it almost two years and have yet to replace the battery. My recommendation is BUY IT...

I have been using for three months no problem at all.