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tds meter (ppm of total desolved solids)

T

tyler_ hobbyist

New member
Can anyone tell me what the importance of a tds meter is and if I have autoflowers how much ppm of tds should I have? I bought a pH meter and a free tds meter came with it. Does the ppm differer from strains? Thank you for any advice
 
There really isn't a "correct" PPM because it can be affected by a lot of things. If my starting water is 250 PPM and I add 300 PPM of nutrients, I have a total of 550 PPM. But if I started with 100 PPM water and added the same amount of nutrients, I'd have a total of 400 PPM even though the plant is basically getting the same levels of added nutrients. Then consider I might start with muddy water. It might be 1200 PPM even though it has really low levels of nutrients. So if I add 300 PPM of nutrients to that water I'd have a total of 1500 PPM and it wouldn't really have higher levels of nutrients than the water with a total of 400 PPM.

BUT if I added 1500 PPM worth of straight nutrients from a nutrient bottle into pure water, it would kill the plants overnight at 1500 PPM.

So there's no ultimate "right" PPM, because it depends a lot on "what" is actually making up that PPM.

I've always used PPM meters to measure the difference over time, with my particular plant and setup. So if the water goes in at 600 PPM and plants get burned I know I need to use less nutrients next time, which means it should be less than 600 PPM next time. In hydro, it can be used to tell if the nutrient levels are going up or down in the reservoir each day, so you know whether to add more nutrients or just plain water to maintain the PPM.

But in my experience it doesn't seem very helpful to compare absolute PPM numbers with other growers, because it's like comparing apples to oranges a lot of the time (with all the different types of water and nutrients).
 
The tds and pH pens are tools for telling me how my growing medium is doing. The tds allows me to tailor nutrient concentration during the grow just like the pH pen lets me know if I'm to far acid or basic. Simple tools but very important to a good result. On my RDWC hydro system I usually run 500-1000ppm during a grow but I have pushed it as far as 1500-pretty thick.
 
http://www.gyostuff.com/What_PPM_Scale_To_Use.html

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Yes, completely! Some growers prefer EC, but it has the same problems as I described with using PPM. And many people end up converting EC to PPM anyways (since everyone else including nutrient companies usually use PPM) which adds one more variable.

And just like you said, different TDS meters measure PPM differently, making it even more like comparing apples to oranges!

There's definitely a lot of information to be gleaned from TDS meters, but when it comes to the practical use for hobbyist cannabis growers, I've found you often get the best results comparing your results to yourself, instead of necessarily comparing to other people's measurements, just because there are so many variables like you said.
 
Thanks 9fingers for posting that. I started writing out an explanation of conversion rates at one point and decided I had better things to do ;). Stick with posting EC or otherwise always mention your EC/ppm conversion rate, which should be specified in your users manual or else online.
It's as Nebula said. If you go out looking for the magic ppm numbers you'll never find the answer, or if you do it will be wrong. Lots of variables so at best you'll get a very rough guideline range.
It can be very useful to have that meter though. I use one when mixing all my nutrients and write down all those mixes in my journal. I hardly ever look at the journal again, but over the years I've mostly figured out the ppm each strain prefers. If we were growing the same strains in a similar setup I could give you a pretty good idea of what ppm amounts work. 50 ppm too high in my feeding schedule can make the difference between perfection and minor nute burn.
 
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My TDS meter gives me as starting number for my tap water.

I add my nutrient schedule for the current week in the grow cycle. That gives me a grand total number of tap water plus nutrients.

I water my plants.

Plants do good, they get the same number next time
Plants look weak, they get bigger number next time
Plants look toxed they get smaller number next time

I can do that with any meter
 
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