Is it normal for PPM to fluctuate day to day?

[h_phonix66]

Hey guys, it's my first time posting here and just wanted to get some insight on something I've been tracking..

I'm growing some lettuce in a DWC setup and I've been keeping a close eye on my PPM. My last reservoir change was a week ago, and I've been checking the PPM twice a day. The numbers are a bit confusing..

My starting PPM was 642. The next day it was 635, then the day after that it was 644, and yesterday it was 660. I've been writing everything down, which has been helpful, but I'm trying to figure out if this fluctuation is normal. In my head, I'd expect it to just go down as the plants consume the nutrients. Is it common for the PPM to rise and fall like this? Any advice would be appreciated. Thanks!

 

[Denison W]

Welcome! I had the same questions when I started growing basil in DWC last spring. It's normal for PPM to go up and down a little. Plants often drink water faster than they take in food, so the numbers can rise. Adding plain water helps keep things steady. Are the leaves curling or turning brown at the tips? That can be a sign something's off.

 

[Kevin_Winnicot]

When I started logging every reading, I saw the same thing.... up, down, up. Thought I screwed up mixing, but it's just how it goes. As long as your plants look good, don't chase the numbers too hard.

 

[JackPumpkin]

The PPM never stays perfectly steady because the ratio of nutrients to water keeps changing. Warmer temps can make it drift up, cooler temps bring it down. The best habit is topping off daily with pH balanced water and doing a full change once a week or so. How stable has your pH been along with those PPM readings?

 

[fabs]

The numbers are narrow. Most meters have 2% accuracy of the full scale. If the meter is 0-1999 ppm then that is +/- 40 ppm. All readings overlap. There is also temperature consideration. Is the temperature stabilized. EC/TDS readings change with the slightest change in temperature. For example, ATC uses 1.9%/oC. It is calculated at the reading and not full scale. For example at room temp (25 oC) a reading of 100 ppm would show 98 at 24 oC and 102 at 26 oC until the temperature has stabilized and corrected. Once the temp is stable then it would show 100 ppm.