You need to use better water. At least pick up one of those Aquarium Pharmaceuticals tapwater filters, which is a deionizing filter good for about 100 gallons of water. They're cheap (25 or so). Better still in the long run, invest $150 or so in a permanent Ro/Di system.
In the meantime, feed your fish less--once every 2 to 3 days--for a while. Over time, you can return to feeding daily, but only feed very little.
You might also reduce your lighting period each day by a few hours.
Finally, spend $3 at Target on a good turkey baster. Use it to suck out red slime as possible, and use it to squirt the slime off of your corals and any sessile invertebrates. It can choke them out.
Good luck!