Trying to understand PPM better

Trying to understand ppm a bit more. Put in all my nutrients from Fox Farm and they say I should have a ppm of 1680 - 1960, but the ppm meter is really low. Like 300 - 500 it keeps jumping around. Is the ppm stick I got wrong or do I need to some how raise it? I’m on week 4.


If you’re reading it’s jumping around I will try changing the battery frist. 2nd you can verify your meter in a standard conductivity solution .


Thank you for the advice! I have solution I use for my blue lab ph pen. Would that be compatible with the ppm tester?

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No , you will need conductivity solution. You can buy it on line. 1000 ppm would be a good number.


Thank you again for your help! :grin:

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Your blue lab pen is submerged to the keyboard, that would be a no no with my cheap pH pen, is the entire blue lab pen waterproof?


I have same pen.


There are different measurements for “PPM”. There is EC - Electro Conductivity which is what the “real” measurement is. Then there is TDS which is EC x 500, then there is PPM which is EC x 700. Right now week 3 flower im at 910 TDS, or 1274 PPM or 1.82 EC its the same.

Meters can vary with what their multiplier is from EC to give you a TDS or PPM reading. This confused me as well so i used the numbers to correlate plants good, plants want more food, and plants want less food. The actual value matters, but the trends stay the same so you can watch and build that correlation in actual number for yourself.

Im a hydro RDWC grower and use an active monitor.

Always start at half what it says. Then -

Plants want more food number goes down as plants drink and PH goes up, increase food mix. The plant food is getting less concentrated as they drink.

Plants want less food number goes up PH down, give less food and lower the number. Food is becoming more concentrated as they drink.

Number stays the same PH stays the same as they drink, thats equilibrium, the goldilocks zone. Its challenging to stay here because it moves after a while, so i find it then stay close by watching it and keeping track.


Note the 700 scale is used by FF. Most nutrients in the USA use 500.
You should be able to use the MODE button to toggle between the various scales EC, 500 and 700. Usually there is an indication on the screen as to which scale is being used. I could not find that in the photo.
If EC = 1, it is the same as 500 using 500 scale and 700 using 700 scale


:arrow_up: this. Thanks for pointing it out beardless! This is how people over feed with fox farms. They think they’re feeding 1000ppm when they’re actually feeding 1400ppm on 500 scale.



The ppm measurement at the top of the chart assumes that you are using the solubles in the purple section of the chart. If you only mixed Big Bloom and Grow Big together then the ppm should be less than listed because you didn’t include the Open Sesame.

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What medium are you growing in, soil or hydro?

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Sorry for the lack of info, but I am using soil

I should’ve mentioned I was using everything in the week 4 column, I’m sorry

Thank you for letting me know that! I just purchased a new PPM tester and was still getting a low reading, but then saw that there are 2 different scales. I found a conversion chart on a different post saying I should be around 1250, but I’m at 1024. I think that may be close enough, I don’t wanna burn my plants from the nutrients

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It definitely is a confusing process haha, I can’t imagine how much harder it is growing in hydro. Thank you for help :grin:

FF feed schedules tend to be very heavy handed.
Week 4 calling for EC of 3, converts to 2100 and 1500 on 700 / 500 scales respectively. Personally that is nuts. Half that EC at that age is adequate. FF theory is overfeed then flush and repeat. I used to use FF Trio. It works but flushing is required.
A couple of schedules - growth stage PPM for reference

I put this together when using FF nutes


Wow thank you so much! Thank you for sharing those! If I’m under the PPM range what more do I add? The FF schedule has me adding in like 6 different bottles and if I’m under I don’t know which one I should add more of.

You dont really. You should either follow the schedule with the parts mentioned or dont. The NPK needed for complete nutrition is based off the use off all components listed and anything less leaves your plants wanting more or lacking things completely.

For the most part you can slide by using grow big, big bloom and tigerbloom. And if thats the case and you dont have the rest of the line up just use what you have in proportion to what the schedule says. And if your ppm is lower than you would like or need then gradually increase all 3 respectively until your ppm is met.

When I used the trio the only thing I added was Silica. Of course a good microbe product would be beneficial. A good many fox farm trio users do not go beyond what I described.

Being under FF PPM range is what I was recommending. When the feed schedule is followed you basically get massive amounts of salt built up in the soil which requires it to be flushed and reset. Salts / nutrients build up in the soil because the plant can not consume all that is given. If this is the case why in the world keep giving more than it needs. It just doesn’t make sense to me. This is just my opinion. Many may disagree. Then on the other hand there are a lot of former FF users. There is a reason why one changes nutrients. I went from FF trio to Advanced Nutrients and now to Jacks for the past 2 years.