This is from an article published by RANDY HOLMES-FARLEY, Ph.D.
I multiply the recipie by 5 to make 5 gallons at a time.
Recipe #1
In this recipe you make 3 stock solutions. Two are used frequently, and one is only used occasionally to balance things out.
You can mix and store the solutions in any all-plastic or glass container. Plastic 1-gallon milk cartons (typically made of HDPE, high density polyethylene) can be a good choice.
Part 1: The Calcium Part
Dissolve 500 grams (about 2 Ã"šÃ‚½ cups) of calcium chloride dihydrate (Such as Dowflake 77-80% calcium chloride) in enough water to make 1 gallon of total volume. You can dissolve it in about Ã"šÃ‚½ gallon of water, and then pour that into the 1 gallon container and fill to the top with more fresh water. This solution is then about 37,000 ppm in calcium.
If you use an anhydrous calcium chloride (such as Kent's Turbo Calcium or Peladow Calcium Chloride (a brand sold by Dow that some believe may just be a dehydrated equivalent of the Dowflake), then you should use about 20% (1/5) less solid calcium chloride to make the recipe. Note that the solution will get quite hot when dissolved anhydrous calcium chloride.
Part 2: The Alkalinity Part
Spread baking soda (594 grams or about 2 Ã"šÃ‚¼ cups) on a baking tray and heat in an ordinary oven at 300 Ã"šÃ‚°F for 1 hour to drive off water and carbon dioxide. Dissolve the residual solid in enough water to make 1 gallon total. This dissolution may require a fair amount of mixing. Warming it speeds the dissolution process. This solution will contain about 1,900 meq/L of alkalinity (5,300 dKH). I prefer to use baked baking soda rather than washing soda in this recipe as baking soda from a grocery store is always food grade, while washing soda may not have the same purity requirements. Arm & Hammer brand is a fine choice.
These two solutions are added as frequently as necessary to maintain calcium and alkalinity. In some light to medium demand aquaria, you may not need daily additions, especially for calcium. Nevertheless, unless testing shows that you should do otherwise, add equal amounts of Parts 1 and 2 over the course of a week.
Part 3: The Magnesium Sulfate
Dissolve a 64 ounce container of Epsom salts (about 8 cups) in enough purified fresh water to make 1 gallon total volume. This solution is added much less frequently than the other two parts. Each time you finish adding a gallon of both parts of the Recipe #1, add 610 mL (2 Ã"šÃ‚½ cups) of this stock solution. You can add it all at once or over time as you choose, depending on the aquarium size and set up. Add it to a high flow area, preferably in a sump. In a very small aquarium, or one without a sump, I'd suggest adding it slowly; especially the first time you do so to make sure that corals don't get blasted with locally high concentrations of magnesium, sulfate, or any impurities in your Epsom Salts. The first time that you add it, you might add a small portion and make sure there isn't any problem before proceeding to add the remainder. This solution contains about 47,000 ppm magnesium and 187,000 ppm sulfate.