TDS/EC/PPM is a measurement of the presence of dissolved solids (fertilizers) in your feed or your runoff. The 3 (TDS, EC, and PPM) are different ways of looking at the measurement of those dissolved solids.
Feed more for a higher PPM. Feed less for a lower PPM. Maintain PPM as close to 1,000 as you can through the grow.
Many of the members here use Jack’s 321, the Fox Farm Trio, General Hydroponics, or Advanced nutrients.