IMHO get a 3 gallon equivalent air pot and plant directly into it.
OF soil and mix it with another soil.
OF is a great soil but is a bit heavy by itself. That's what I'd recommend. As to your water. A ph meter is good for just that, ph. Ask your water utility company for a TDS read out and research whats in there. You may find the culprit thats either locking out nuets or find there's nothing wrong and you got great water. Either way its always a good idea to know exactly what your feeding your girls. 
