Salt will usually increase GH & KH. Since the product you are asking about is labeled as "Water Softening" it must actually decrease the GH & KH. This is good if your GH and KH are already at the upper acceptable limits for the kind of fish you keep. That is why I asked you what your GH was. Goldies usually prefer 100-200ppm. So if your GH/KH was already well over 200, then yes, you would probably not want to increase it.
That being said, I personally have no experience with this product as I have very soft water as is. I went to the Mortons website. Direct quotes from their site...
Q: Which Morton products can be added directly to a koi pond or fresh water?
A: When salt supplementation is advised, Morton recommends using Morton® White Crystal® Solar Salt or Morton® Canning and Pickling Salt for fish ponds and fresh water aquariums, as these products do not contain additives. Note that it may be advisable to make a solution from the salt before adding it to the pond or aquarium. Please see your fish expert or veterinarian for the proper use of salt in a pond or aquarium. Back to Top
Q: Which Morton products can be added directly to a salt water aquarium?
A: For salt water fish, Morton recommends using commercially prepared seawater (marine) mixtures, as they should contain the proper ratio of trace minerals. Morton does not make a product specific for salt water aquariums. Morton® White Crystal® Solar Salt is not a sea salt obtained from evaporation of ocean water to dryness. It is a higher purity salt, and therefore cannot be used to make seawater for salt water fish without additional trace mineral supplementation. Please consult your fish expert or veterinarian for the proper use of salt in a pond or aquarium.