RO water does not have the nutrients and minerals that tap water does. It is too pure for freshwater fish, they need certain things in their water to be happy, not to mention it may have caused an unstable pH (where it doesn't in saltwater tanks due to substrates and live rock) because unless you have crushed coral substrate, there was no buffer. The plants also need the nutrients and minerals that come in the tap water unless you are dosing it with other additives. When using RO in fresh water you MUST add some stuff back before putting it in the tank. So to answer your question, yes, you need to go back to using water from your tap.