Unless the GH is low, I wouldn't add any epsom salt or calcium chloride. If the water in your pond is all rain water, water that has come from a water softener, or deionizer, then you may need the epsom salt and calcium chloride. There are some natural water supplies, like one that I am familiar with in NC and another in WV that have zero or near zero GH and have to make additions. If your water is this low in GH then additions would be necessary but the additions should be in response to changes in the GH. A certain amount of calcium is needed to react with the carbonate released in the process of baking soda neutralizing acids in the pond to keep those carbonates from driving the pH up, by making a precipitate of calcium carbonate, a form of limestone, chalk, marble, etc, which are not soluble at those pH values. For my 4000 gallon pond, I add about 5 cups of baking soda with every water change which accompanies the filter backwash each week.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard