Whoops...missed the question.
Well thats a little tough to answer...or at least for me it is anyway.I'm pretty new to the salty side thing myself.
I think if your are not keeping corals it will be ok.Inverts I just don't know enough to reply about.Small amounts of metals can mean death so I guess that will depend on the tap water quality.
[I'm just typing what i'm thinking so I also expect a correction or agreemeant form somebody who actually knows]
You certainly will not be the first to start with tap...Heck even I did that with the 90,but I saw the need for RO
so it was a no brainer here.My bud also started with tap and has the situation you discribe (low lights,just normal NO aquarium hood) and he still had a pretty bad algea problen setting in.He just did his first PWC
with the RO
so I can't really report if it helped or not just yet,but I'm confidant it will.
The store I was riding to sold both premixed salt and fresh RO
.The cost was 75 cents and 25 cents per gallon respectivly.I bought the fresh and mixed it myself.
For ten gallons thats $2.50 and thats for a complete start up in your case.PWCs will be even cheaper.
Long post a bit longer,You will "probably" be just fine....but at the price of RO
in such small quanities I'd start with the good stuff right off the bat.