I have a 55 gallon saltwater tank with four clown fish and a goby, it has been running for about a few months I already have brown algae at the bottom and on the glass. But my water level is starting to go down about an inch already from the top and wanted to know what is the proper way or what to use to top it off? Plain tap water ? Or distilled water? I’m not interested in getting a top off system, I am just getting so many answers I just don’t know which one is the right one- thanks in advance!!