In addition to removing Chlorine...the RO/DI water will also remove the negative and positive ions...such as nitrate, silicates, phosphates, the TDS as mentioned above, and numerous other hard metals.
Most of the items a system will remove are nutrients for micro algea to consume and flourish.
Also, this is a very expensive hobby with continuous on going expenses for maintenance and such...one needs to weigh everything prior to venturing into this...without being able to purchase things in which you need, it will usually be a failure and very disappointing....been there done that. Now I pay
[hr]
, truck payment and aquarium stuff...then all those optional things...food, electricity, etc...