Mix all of the ingredients together and transfer by the spoonful to the silicone mold. If you have sensitive skin, you might want to wear rubber gloves while pressing the powders into the mold. The citric acid will cause the mixture to harden within an hour or two. Use 1-2 tablets per load – how much you use will depend on whether or not you have hard water. For hard water, you might need 2, so it could be a bit of an experiment at first.
Store them in an air-tight container.
If you use white distilled vinegar as a rinse aid, you can make citrus infused vinegar or add 2-3 drops of lemon essential oil per load to aid in the cleaning power and make it smell better. You could also add lemon juice to it instead of the essential oil.