What ppm to start feeding

So I've been feeding at usually 500ppm. Do you guys let it drop lower to feed? Growing in fox farm happy frog. How do you guys know when its time to feed?

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I have never measured PPM in soil

Herb & Suds said:

I have never measured PPM in soil

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Then how do you know when to feed?

Ayokiwi717 said:

Then how do you know when to feed?

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I feed constantly and base it on the plants needs
Color and the way leafs are associating to the environment are good indicators
After a while it just becomes second nature like driving a car