good plan. 10 is overkill in all but the most hardcore sps tanks. I am running my mixed reef with some pretty demanding sps corals at 8. I have done much less on tanks without corals or with low light corals. Sometimes down to 5.
don't panic! Water changes with good water and salt never hurt. Diatoms won't kill anything, but they do look cruddy. When the silicates burn up, so will the diatoms. (diatoms are actually tiny glass structures, they look like little glass snowflakes under a microscope - really cool.)
I buy RO water right now too because we don't have a good place for a unit in our loft. They are a good investment and should remove all your silicates. Now just use a good salt. Be patient. The tank is ok.