Talk to me about PPM

Good Morning All,

I am looking for some clarification on PPM’s. What should I see. My last feeding, before I fed I did a slurry test. The PPM’s where right around 300, I am using NFTG’s and the nutrient mix measured around 800ppm. When I checked the runoff after feeding, one plant was close to 2000ppm and the other was around 1500. The PH of both the slurry test and runoff is 6.5.

Does that seem right?

It’s been a few days and they look fine and are due another watering. The NFTG says schedule is Feed Feed Tea, Feed Feed Flush. I am afraid to feed again with the PPM’s that high. My other grows I did not monitor the PPM’s as closely and followed the schedule of feeding and the plants seemed fine, but I still want to make sure I am optimizing everything


What soil are you in? If you have younger plants and you are in Ocean Forest, for instance, then the nutes won’t have been taken up from the soil in the bottom of the pot and you will get a higher runoff PPM.

Doesn’t seem likely that you would have a salt buildup with the stable pH.

Sorry, I don’t know what NFTG means.

1 Like

I am in Fox Farm Happy Frog. NFTG - Nectar For The Gods Nutrients. The plants sprouted on 3/26/20. So I am not sure if the roots have yet reached the bottom. I started them in their final pot. 5 gallon fabric pots.

Have a picture of the plant(s)? I wouldn’t expect that either from a 5-week old plant in Happy Frog. Kind of strange. Is it correct that you’ve just recently started feeding?

Are you using the correct scale, you should be using the 500 ppm scale.

@Arborfarms I am just using a PPM meter and getting a reading…

@MidwestGuy Here are the pics. The larger one has some turned leaves, but I believe that would be due to me manipulating the plant to LST.

I only fed once, which was on Saturday.

1 Like

I’m stumped. Let’s ask @Myfriendis410 to weigh in.

1 Like

Your ppm is high because your soil already has nutrients in it and your adding nutrients on top of it. The difference between the two could be from many variables. One could just have less of a volume of nutrients in the mix, odd but it is a possibility. Another could be the time frequency of when the runoff was measured, measured too soon you will have low ppm’s. I would measure without adding bottled nutes first. Once that starts dropping off to around 600ppm that would be when I start adding nutes to get the battery (soil) recharged and the ppm’s back up.


Doesn’t seem to be anything wrong. Just hold off on the next feed, do straight water (pH’d ofcourse or distilled,r/o) and check ppm again see if it’s eating. One skip of fees for the better isn’t a really big deal. Btw I’ve had ppm’s around 2500 before with just ffof soil runoff.

1 Like

Plants look fine, suspect there may have been a measurement error. Keep an eye on your runoff numbers for now.

1 Like


So in general, if i go to feed and the nutrient mixture is 800ppm, when I measure runoff, ideally it would be less than 800ppm showing the plant has taken up nutrients?

1 Like

That is correct unless in soil. That may keep you at a higher baseline than say coco. If in something like coco then I flush when my TDS gets up above input TDS. I’ll run water and monitor runoff until it gets to where I want it.

1 Like

Hey friend. I have been watching your activity on these forums and feel you will have the best info for me on this. I feed every other watering and keep my PH around 6. I am using soil (happy frog) and my ppm at half strength fox farm trio is in the neighborhood of 1300 ppm. Is it acceptable when in soil for my runoff ppm to be in the neighborhood of 200 ppm HIGHER than my input ppm? Thank you for your help. I want to make sure I am not over feeding.

I typically feed in veg around 900 ppm (with FF trio) and bump up to 1,100 ppm or so in flower. Soil buffers differently than coco so I usually let the TDS rise to around 2,000 ppm with continuous feeding then water only until runoff gets down to around 1,000 or so. I think you are fine.

Remember to flush when the schedule recommends it and FYI most of the grow schedules for FF are in 700 scale and not 500 scale so numbers look higher on the published chart.


Thanks so much, my friend. This helps a lot.
Have a wonderful day.

1 Like