Thanks - that's a great page. I think I'll switch to using EC as that seems more reliable.

I just wanted to follow-up on one point. Some instructions I see say add xx ML of nutrients per gallon - then they say the nutrients should be yyy EC or PPM. But when I mix the nutrients they don't add up to the EC/PPM indicated (even accounting for the starting point of my water). So, which number do I pay attention to - the amount of nutrients to add to the water or just keep adding until I get to the desired PPM?

I usually stay on the low side and watch the plants. They will tell you if they need more fertilizer. It is not an exact science because all the variables like: temp, light and stage of growth. Example: young plants need less. I start at the low end of the EC range for young plants.

ppm is actually just calculated from EC. If you have a ppm meter, it really measures EC and converts in internally. You can do the same with an EC meter. EC x 640 = ppm.

you want to reach the PPM or EC specified. the maker of my nutrients specifies 1800ppm for adult plants and 1400 for seedlings. I run the adult plants at about 1600ppm. and I only check it about once every 2 weeks. the larger reservoir you have, the less often you'll have to check and adjust it.

you'll want to keep it up where they specify, but I've gone on long vacations and when I got back the PPM was around 300 and the plants seemed fine. they won't grow as fast, but as long as they keep getting water they should be ok.

dear sir, i am starting to grow lettuce in aeroponics technique please let me the nutrient recipe. tahirmalikawan86@yahoo.com

My water had too high PPM and it negatively impact the seedlings so I only use half strength when they're small.