Fox Farms nutes and ppm

Going on 4th week of flower, according to the fox farms feed chart, for 8 weeks ppms should be 2150-2310, using their recomemded amounts my ppms are only 1600 and that includes my water at 170 ppm, should i run with the chart or do i need to increase some thing? been feeding according to chart and plants are doing fine, with no sign of nute burn. 3 purple kush, and 3 durbon poison.

The pens that register ppm can be calibrated differently giving you wonky readings if you don’t know how your pen is calibrated. In general there are two different standards for measuring ppm. One based on a 500 scale, the other a 700 scale.

The fox farms chart lists ppm using a 700 scale… Many ppm pens sold in the United States use a 500 scale. If your pen uses the 500 scale you need to adjust the numbers on your feeding chart.

You can easily convert the EC scale on the fox farms chart to a 500 scale. An EC of 1 = a ppm reading of 500. With a 700 scale a EC of 1 = 700 ppm.

On the feeding chart the 2100 ppm corresponds to an EC of 3. On a 700 scale 3x700 = 2100ppm. Using a 500 scale 3x500 = 1500ppm. My guess is your pen is based on 500 scale and you are getting exactly the reading you should be getting.


Awesume help, who would have known that, thank you

@MrPeat uses FF whole line. Will likely have some advice now that I tagged them in.


Im going to feed per chart, they arent starving and no burnt tips, so i also beleive its a ppm dif in the measuring devices.
Thank you, ill take any advice i can get.


The chart is good so you don’t over feed but it isn’t marijuana specific. It’s at best a guide for what would be too little or to much for any plant. Take it slow and easy with nutes, that’s my advice. Start at 1/2 or even a quarter dose and build your way up. Make sure you follow the flush guidelines to the letter. (3 times the volume of your pot in water.) Pro tip: you will need calmag

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If you don’t use every nutrients listed for said week, you will be lower for the PPM’s than they have listed.

Example: Week 4 uses 8 different nutrients. So if you only use 3 nutrients, you will be way lower than the PPM’s.

Does this make any sense?


I use exactly what’s on the chart, except the foiler spray, two times a week. And I flush per the chart, and I’m flushing rite now. I get my ppm down to 500 ish, wait a cpl hours and give them a light feed. I use cal mag every water and feed, I use 1 tsp of epson salts per gallon 2 times a week

Here is a chart for 500 scale meters.


Why does this chart only go to 8 weeks? Hmm I’ll start using this chart next feed


Ahh, I got it figured, 500 ppm chart week 1 of flower over laps week 5 of the chart I’ve been using, so it’s the same amounts, just converted to the 500 ppm chart

I changed it to show weeks of 18/6 and 12/12. People were getting confused and thinking they had to switch to flower on week 5. If you’re growing a 10 or 12 week strain, just continue week 8 of flower.

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My pen always shows EC = PPM x 2

For example

PPM: 1,000
EC: 2,000

Is this not correct?

What does a light feed mean? And what does epsom salt do?

Correct, it isn’t hard but some find it hard to grasp. If they just went by ec there would be no confusion.

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You just saved me a whole bunch of figuring :sweat_smile:.

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Well said. EC is the answer. I don’t even use a feed chart. I feed by runoff’s. Keep a runoff’s of 1000-1100EC and feed accordingly. Simple math.

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