Which water to use is a matter of priorities. Tap water in the GVRD is generally good enough for a reef, unless it isn't on some particular occasion.
Construction or some other form of contamination could wipe out your whole tank. Maybe tomorrow, maybe in 20 years.
If you have 2 x $5 frags and a damsel, maybe it doesn't matter. If you have $500 worth of coral that you've grown from frags, maybe it matters.
So for the cost of a RO unit, you eliminate that possibility. It's peace of mind.
Sure, nobody wants to spend an extra $200, but if it saves your tank one day, you gotta think it's worth it.
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Brad
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