Regarding ideal levels of nutrient and pH - this is more of a range than a specific number and is affected by many factors, most importantly the type of plant being grown (Indicas and Skunks can make use of more nutrient that Sativa hybrids), and the medium they’re grown upon.
Hydro mediums like rockwool are given feed water with a much lower pH than would be given to soil.
Soil is generally healthiest between pH 6.0 and pH 6.5
Hydro is usually around pH 5.6 to pH 5.9 (since hydro mediums that tend to raise the alkalinity of the solution slightly).
Aeroponic is a subcategory of hydro (since the soluble nutrients are the most important part), but since it uses little or no grow medium, practitioners may not need a starting pH quite as low as when roots grow in rockwool. In most aero systems, the plants are couched in a small amount of medium, with their roots trailing free inside it.
Therefore, pH 5.8 to pH6.0 is probably ideal in aeroponic systems. If there’s quite a bit of rockwool involved, it could go as low as pH 5.7
Bear in mind that different plants may react favourably to slight differences in pH, so when changing the level of acidity in feed water, growers should be sure to observe plants closely during the first two weeks of the change.
EC (electrical conductivity) is the basic way of measuring the concentration of soluble nutrients in feed water. Absolutely pure water is not a particularly good conductor of electricity, and the more dissolved minerals contained in water, the better it conducts. Measurements like PPM, CF and TDS are based on the EC reading. EC is the measurement used for the plants that grow in the Museum.
Seedlings should start out with very low EC – 1.2 - 1.4
Larger vegetating plants, rooted clones and mother plants can be given higher levels of feed – EC 1.4 -1.6
In the first half of flowering, plants should start around EC 1.6 and be raised up to EC 1.7-1.8 by the middle of flowering.
In the last weeks of flowering, Sativa hybrids will usually be fine with EC 1.8 -1.9;
Indicas and Skunks can thrive with higher levels of nutrient – up to EC 2.0 - 2.2 (and generally need more nutrient in order to build their thicker buds).
I go with higher EC 1-1.2