I wouldnít do anything if I were you. Neocaridina will do just fine at a ph of 6.6. Many breeders use water from 6.5-7.5 with higher to a point being fine. My guppies did fine at this ph as well. Hardness is more of a concern for both so if you have a gh of 6-8 or higher all should be just fine. If you did want to adjust your kh up I would just target a specific kh in general and make sure itís added to new water at water change. For example if using ro water for water changes you could use CACO3, CASO4 and MGSO4 with a target of 4 kh and 8 gh and all would be right in the world. If using tap I would use a liquid gh/kh test so you can see within 17.6ppm what those numbers actually are in addition to a tds meter. In my remineralized water I use the above mentioned compounds as well as 20 ppm potassium from KCL as well as a small amount of micro nutrients, iron etc.
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