I am not a stranger to saltwater aquariums but not an expert either. I was able to acquire a 75 gallon (predrilled), uv filter, sump, 2x odyssea 175w mh lights, return pump and maybe 1in of sand and maybe 10lbs live rock, etc... When they arrived at my place apparrently somebody forgot to tighten the caps on the water jugs and ALL THE WATER spilled but still had just 10-15 gallons of water left over. I am not complaining considering I got everything for $200!! So I have the fish (chromis, clown) in a little 20 gallon tank in the mean while. This tank has been running for 6 months from what I was told
So here is the dilema I only have two options available to me due to my budget (have a son in the oven).
I hate using tap water because I always used a ro/di that I no longer have. Anyways, use the 10-15 gallons and make the rest with tap water (using amquel). And in a week or two start doing water changes with filtered water
or
I have a buddy I gave my 55 gallon tank to when I moved however he no longer wants to do saltwater ( too hard

) so the tank has 2 fish that are alive and "well" (if you will) but nothing has been running for at least 2 months! But the tank still has at least, when I gave it to him, 75lbs of live sand, and like 50 lbs of live rock. The tank is not cloudy but has a green tint to it. And in a week or two start doing water changes with filtered water. This tank ran for about 6 months at his home, I know because I did most of the maintenance for a while.
So much for keeping it short
Forgot to add with the second option: I won't use all the water just so I could yes less treated tap water