This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred, so parts per million or ppm means out of a million.
One ppm is equivalent to 1 milligram of something per liter of water (mg/l)
Its a way to measure. Its actually a Parts per then what ever notation (million, billion and trillion are commonly used in the chemistry world)
So if you understand that correctly, its truth to say a higher PPM is a more concentrate solution.
So we as growers can use the PPM scale to measure our nutrient solution to check in on its concentration, you know we dont wanna burn our babies!
As when to add and what strength varies on strain and also stage of growth. BUT one thing they all have in common is that you would not feed any plant 1000 PPM concentrate of solution to a seedling.
There is alot to know about nutrients too. For each diffrent stage of growth the plants need diffrent N-P-K values. Its the three primary macro nutrients: nitrogen (N),Phosphorus (P), and potassium (K).
There is also secondary nutrients and macro nutrients. Plants need all these and doing hydro ,. its the growers part to make sure these are getting to them in the right concentrations.
So if you have never grown before, i Suggest reading into somethings and really understand what your getting your self into. It will guarantee success and be a really good experience.