>... Built in skimmer...
That sounds like a cheapo... any info on it?
>..using the Calligan water from my local walmart.
Got a TDS meter handy to test the amount of junk in the water? You may want to "invest" in a reasonably price RO filter (~$100 from Costco) if you have bad result from your walmart water....
>...Bio balls,... My nitrates are showing 0...
I am a bit surprised. Either you do lot of water change, or you have a very low bioload, or your test kit is not good... what brand is the nitrate test kit?
>...The way I did it in the past was to scrub it in the sink using tap to rinse. I know the tap is not good ...
The small amount of tap on the rock will not cause that much of a problem, so it is fine thing to do if you don't mind about the possible problem of shocking the critter on the rock with fresh water. I usually get a gallon of water from the tank, and after scrub the rock, shake the rock in the water to get the algae loose. Discard the water afterward.