The added calcium and magnesium probably in the water won't hurt the lettuce, and if your farm water is yours, it would be worth analyzing it for a few bucks to know for sure. Cutting back too far on the nitrogen will reduce the growth rate and the other stuff in the water probably isn't doing anything much to add to nutrients, just raising the salinity. Wow, I just noticed, you said the pH down brought it from 300 to 600 ppm, ufff. When you top off, use rainwater!

It all depends on where you are with the current formula. Probably you want to shoot for around 115-120 ppm for nitrogen in there and just let the rest fall however it falls.

This post was edited by PupillaCharites on Tue, Sep 3, 13 at 16:46

My problem is I am using a " complete fertalizer" it has cal and mag already in it. How would I ever measure the strength of the nitrogen alone week to week?

Plants look good, I am just trying to make sure I am giving them as much as they will take and not too much. I am looking for a local test site for our water.

Well, somewhere I read the dedication in some book, "The plants will be the final judge" but you wanted to optimize.

For the test lab, you might want to mail it instead to these guys who really know what they are doing, $36 bucks abnd the kit is sent free:

Water or Fertilizer solution test