Experienced beginner!

[ron v]

Not salt. Baking soda & epson salt as EMC said. Or easier...go to pet shop and buy a "cichlid salt" There are several brands. The intended use is for rift lake cichlids that need very hard water. You would only use a little. Or you could mix a little of your tap water with distilled... As for supporting fish... it depends on what fish LOL.... Always questions... Some of the south american fish live in very soft water so it would take much for them.

[bmlbytes]

I don't think I would want to mix tap water with it, it would give that unknown variable. In an experiment you want everything as controlled as possible.

And what is the difference between epson salt and aquarium salt?

[ron v]

Aquarium salt is table salt. sodium chloride. Epson salt is magnesium something (I don't remember the compound)LOL. The hardness of your water is made up of Carbonate hardness (you get that from the baking soda) and general hardness (that's where you need magnesium). The "cichlid salts" I mentioned earlier have these things plus several trace elements that are good.

[emc7]

Epsom is Mg Sulfate. The cheap cichlid salt recipe is baking soda, Epsom salt and marine salt (Sodium Chloride + a lot of the trace elements). The easy recipe is a SeaChem product. They have cichlid salts, hardest support for planted tanks, and mineral replacement supplements for RO water, to choose from. All of them do the same thing. If you put fish is straight Deionized water, the fish will die. Guess how I know this. A good deionzed water will extract glass and etch stainless steel.