Thank you for your reaction, but as I read it I thought there was a misunderstanding. Maybe I was not quiet clear but the
nutrient solution I am using has as far as I understood no ammonium in it further more I work with a pH of 7 - 8. When the pH is lower the growth is slower. The only problem I really have is cooling the nutrtion to below 30 Celsius as it is often more the 35 Celsius. My lettuce is not soft nor do I have a problem with shelf life as it stays very good when kept cool.
I am very interested to know if there are brands of hydroponic
nutrients with no ammonium an no ureum and where I can find these.
I added a picture.