A TDS meter is a must have tool for anyone looking to grow hydroponically. TDS stands for total dissolved solids, and is represented by PPM (parts per million). In essence, it's a measurement of how much salt and minerals are in a solution. "Hard" water has higher levels of minerals, while "soft" water has lower levels. For reference, water that has below 200 PPM is considered clean drinking water, while anything above 400 PPM is not safe for human consumption.

The PPM of the water in your hydroponic system will vary depending on how many liquid nutrients you've put in the system.

• Seedlings: 100-250 (nutrients should not be added yet)
• First Half of Vegging Cycle: 300-400 (this is usually after you transplant and have just started adding nutrients)
• Second Half of Vegging: 450-700 (your plants will start needing more nutrients as this stage)
• First Half of Flowering: 750-950 (your plants will be eating more as they grow, so they'll continue to need more nutrients)
• Second Half of Flowering: 1000-1600 (this is when your plants will require the most nutrients)
• End of Flower, Entering Harvest: As close to 0 as possible (this is when you'll be flushing your plants)

Just like with pH levels, you'll need to keep an eye on the PPM throughout the growing cycle. When the PPM gets low, you'll want to add more nutrients to your system. Be careful though: if you add too much then your PPM may get too high, which is also bad for your plants. If this does happen, you can lower it by removing some of the water from your system and replacing it with tap water. On average, you'll want to add nutrients once per week. You can find more information in our nutrient and pH guide.

An important detail to note is that a TDS meter does not measure if your water is healthy. Contaminants such as lead or pesticides are not detected by a TDS meter.

Interested in getting a TDS meter? We include one in our Hydroponic Growing Starter Kit, which also includes nutrients and a pH kit. Make sure you also check out our Foody Towers if you're interested in getting into the world of hydroponics.

As always, if you have any questions, be sure to contact us.