 Re: water?
As far as the topping off of your tank... Use freshwater the salts and minerals stay behind during the evaporation process.
Everyone here that has a reef tank recommends Reverse Osmosis water. I do not have that that luxury, nor does everyone else. I use a carbon filter with resin beads and it removes most of the phosphates (algae bloom city) and a lot of the impurities. If oyu search the threads there is A LOT of discussion about this. If you have a small tank and were concerned about water quality you could buy the Walmart Distilled or Spring Water. It is RO water also.
Jim
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90 Gallon glass, 135#'s of rock and 2" sand. 2-250w 20k XM metal halides. 2-95 watt actinic VHO, 4 powerheads, Coralife skimmer. Maroon Gold Striped Clown, Blue Chromis, Kole Tang, Pygmy Angel, Serpent Star, Brittle Star,Gorgonians, Mushrooms, Yellow Polyps, Turbo Snails & Blue Legged Hermits. 20 gal sump with Caulerpa, Mag 7 return pump. | 
