If the nutrients you are using doesn’t have a guideline, here is a basic guideline to follow
Seedlings: 100-250 (nutrients aren’t needed here, hence there’s not a lot of particles needed)
First Half of Vegging Cycle: 300-400 (this is usually after you transplant, which still doesn’t require many nutrients)
Second Half of Vegging: 450-700 (you’ll start giving your plants more nutrients at this stage)
First Half of Flowering: 750-950 (your plants will be eating more as they grow, so they’ll be taking in more nutrients)
Second Half of Flowering: 1000-1600 (this is when your plant’s eating the most, especially if you give it additives)
End of Flower, Entering Harvest: As close to 0 as possible (this is when you’ll be flushing your plants, so you don’t want there to be a lot of particles leftover)
You can always push those numbers a little higher and watch your plants. When you start seeing the tips yellow (painted nails) you know you’ve reached their max and you can back off a little