That plant is too big for its pot. It doesn't look all that bad.
The soil pH range should be centered at 6.7. Any other numbers you have seen (5.8) are meant for hydroponics.
When you mix up your fert solution, check the pH and adjust it to 6.7 immediately before you give it to the plants.
What is your water source? Do you know if it contains a lot of dissolved minerals ('hard water')?