You will be ok without a skimmer if you have enough mechanical filtration with the canisters. Just keep an eye on things.
I would only get away from tap water if you have algae issues. Sometimes it can be high in nitrate and phosphate. If yours isn't, there is no real 'need' to get the RO unit.
I would only get away from tap water if you have algae issues. Sometimes it can be high in nitrate and phosphate. If yours isn't, there is no real 'need' to get the RO unit.