tapwater

So as a newbie, after the cycle was over, I took a suggestion from an LFS owner and made my salt water from city tapwater and reef salt and then changed about 10% every other day for a week. Last night I realized that maybe I have messed up by not using RODI water to mix salt and am not sure...

I was given an already established aquarium. The light hadn’t worked in a while so all the coral died. There are 2 fish and 1 hermit crab. A few days ago I discovered that there are multiple large bristle worms hiding in the sand/rocks. They ate the shrimp I added to the tank and I’m scared...