Understanding ppm

I’m onto my second grow (first one being cut short bc of a move) and am wanting it to be a successful one. I’ve been reading through grow journals and what not trying to learn from the mistakes of others but am still unsure on the topic of ppm. Any advice/info on the subject will be appreciated


PPM is a measure of dissolved solids in water. We use the NACL scale in the US or 500 scale.

When we grow a plant in a medium whether it is soil, coco or hydro, nutrients are made available to the plant via the water we add. So measuring and adjusting the amount of dissolved solids that are available to the plant will help provide adequate nutrients without harming the plant.

The demand for nutrients changes with the size of the plant, it’s point in the life cycle, the conditions under which it is grown etc and this can affect how the plant uptakes nutrients. Experience will help refine those numbers for your individual setup. There are tricks you can use to fine tune how much and when to add nutrients.

Understanding this is central to growing well in substrates like coco or Promix and really essential in hydroponics.


I’m growing in soil at the moment, about a month in and the runoff ppm is 170. I’ve been using reverse osmosis water which is has zero ppm. How would I raise this to make it a sufficient amount for the plant at the different phases of growth?

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First off, let’s get some more info. I’ll add a Support Ticket for you but want to ask and add a couple of things:

What PH and TDS meter are you using? Calibrated?

When you fill out the Support Ticket, please offer up good detail on each point. So when it asks soil? please give us more than ‘yes’ haha. Same with lights, pot size, age of plants etc. This is all important info that I need to be able to see what’s up.

I will say month-old soil should be WAY higher than that and I suspect your meter has a little tiny “X10” in the corner of the display. Just FYI.

COPY/PASTE the below list into your forum post.

Answer these simple questions the best you can.
If you do not know, or do not use something; Just say so; Or post
NA (non applicable)

  • What strain, Seed bank, or bag seed
  • Method: Soil w/salt, Organic soil, Hydroponics, Aquaponics, KNF
  • Vessels: Pots, Grow beds, Buckets, Troths
  • PH of Water, Solution, runoff (if Applicable)
  • PPM/TDS or EC of nutrient solution if applicable
  • Indoor or Outdoor
  • Light system
  • Temps; Day, Night
  • Humidity; Day, Night
  • Ventilation system; Yes, No, Size
  • AC, Humidifier, De-humidifier,
  • Co2; Yes, No

Always try to upload a clear picture of any issues you may have to allow the community to assist you.

Add anything else you feel would help us give you a most informed answer should be included. Feel free to elaborate, but short and to the point questions and facts will help us help you in a more efficient manner :slight_smile:


I’m using fox farm ocean forest for the soil, a honeforest TDS meter which came from manufacturer calibrated . As for the ph meter I’m using a vantacool which I calibrated about a week ago. The ph of the run off is 6.5 and for the seeds I’ve got ak-47 and bubblegum from ilgm. Also the ventilation I’m using in a 4x4×6.5 is two 190cfm 4inch inline fans (intake/exhaust) with carbon filters. No extra co2

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As temperature goes I have it at 72 during the day cycle (20hours) and 68 during night (4hours) with the humidity being anywhere from 45 to 65%