Well fred your PH for hydro should be 5.6 to 6.2. The heater will help if clod but you have many questions to answer.

How are the plant put in there? and then go to the plant problems and fill out the problem form. You will get much more help. Seeing as how you already thought PH was to be 7.0 sounds like you need to learn alot. Fill out he form and keep reading.