Once healthy 6 week old plants looking BAD

Hi guys any help would be appreciated, using easy as organics soil was advised no nutrients needed
PH balanced water 6.5 only nothing added
16 hrs sun
Temp 25-30 degrees Celsius
Humidity 50-60%
Cotton Candy Kush seeds looked good for weeks after going into bigger pots, have changed nothing but started increase in amount of water as they got bigger.
All 3 plants getting the same treatment, first one started to get curled new leaves, then my healthiest plant started getting rust colours spots on the ends of the leaves, and the third one leaves are drooping badly…