I need the least expensive and most durable TDS (Total Dissolved Solids), ph meter and thermometer to use with middle school students. I have to buy between 10-20 so please make them affordable. If it's better (cheaper!) to to have two devices to do all three things that's fine too. Thanks!

Best I could find was $149 with free shipping on Ebay. They have 8 in stock. 


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If you email the seller and ask him to make a deal on all 8 of them, he might do it if you explain you need it for your classroom. Good luck!

Hello, I think it would probably be cheaper to simply purchase two or three devices as you suggested. The cheapest TDs meter I could find for you is the HM Digital Economy TDS Meter, which you can buy in sets of 10 for $13.56. The ph meter is a little trickier, however the Milwaukee pH Tester Model pH 600 sells for $21.95 each at Aquacave. There is no discount for buying in volume, but they do offer free shipping on orders over $175, a figure you would easily reach ordering 10-20 of them. Unfortunately neither one of these devices includes a thermometer, would a simple, low-cost thermometer like the Prestige Digital Thermometer at Amazon work or would you need something more "scientific?"

There are many educational science equipment websites out there that may be helpful in finding exactly what you are looking for. Some of these sites include Sargent-Welch, Science-Kit, and Pasco.