Reddit reviews Worldoor LCD Digital TDS Meter Tester Water Quality Ppm Purity Filter Portable Pen Type TDS Tester(TDS Tester)

Many homebrewers, including I, use this < $5 meter from Amazon Prime.

Testing pH of water is meaningless for your purposes.

Ahhh now I understand...

This is where a TDS meter is needed to check the PPM. An example: http://www.amazon.com/Digital-Tester-Quality-Purity-Filter/dp/B007VK4YY0/ref=sr_1_2?s=industrial&ie=UTF8&qid=1417057910&sr=1-2&keywords=ppm+meter

The ppm depends on the nutrients you use. I have used a few different brands. Most of the ones I have used recommended the ppm to be around 1100. Keeping it at the recommend ppm will ensure you are not under/over feeding your plants. The ppm can vary somewhat but rarely do I have to adjust between water changes. So much depends on the quality of your water. I used to buy reverse osmosis water and my results were very good. I am thinking of getting my own unit just for growing purposes.

Even before I got my meter I followed the directions on the nutrient bottles. I still got good results. Not knowing if they were getting the proper amount of nutrients is why I bought a meter. It's a labor of love and I wanted to make sure I wasn't wasting time and money.

Just a little side note. I cannot tell you which nutrient brand is best. I like to experiment with different ones. But I can tell you that going organic was quite difficult for me. I had to adjust almost everything daily.

These are the models I went with, they've been working flawlessly so far:
https://smile.amazon.com/gp/product/B00YBUH4RC
https://smile.amazon.com/gp/product/B007VK4YY0

Definitely worth every penny, even if they do end up breaking sooner.

Get a 5 stage RO/DI unit from BulkReefSupply (BRS) (http://www.bulkreefsupply.com/bulk-reverse-osmosis-filters-systems/reverse-osmosis-systems.html). You can integrated it directly into your water line under the sink OR you can use the attachments to run it from the faucet, just screw it in and go. There are three lines, red, black, blue. The red is the water input, black is "waste" water that just goes down the drain or you can use it to water plants, and the blue line is the purified water. Get the auto shutoff switch/valve/floater thing (http://www.bulkreefsupply.com/reverse-osmosis-float-valve.html). Get a 20gallon or 30gallon rubbermade container, drill a hole in it, install the float/auto shutoff and connect the blue line. Turn it on and forget about it for a full day because that's how long it takes to make that amount of water. Double check the shutoff valve works first by holding it in the off position and making sure that the unit shuts off and doesn't explode.

Second, you can use RO/DI water for freshwater tanks you just need to use a buffer, here is a good article about that: http://www.liveaquaria.com/PIC/article.cfm?aid=65

BRS has a great video on how to setup the RO/DI unit you just bought, they are < $150 and work perfectly. Get a cheap TDS meter, these (http://www.amazon.com/Digital-Tester-Quality-Purity-Filter/dp/B007VK4YY0/ref=sr_1_7?ie=UTF8&qid=1419568328&sr=8-7&keywords=tds+meter) work great but make sure you order it right away because they ship from hongkong, so you can check the PPM (parts per million) in your water, if it starts to go above zero you need to change out parts of your ro/di unit, could be the membrane or carbon.

edit: lastly, you can drink this water just fine.. BRS even sells a tank to hold pressurized water and a dispenser. it bypasses the "DI" phase http://www.bulkreefsupply.com/brs-add-on-faucet-kit.html

edit 2: i am not affiliated with BulkReefSupply, i just really rely on them for the best info on the net and best products, plus good prices.