I installed PoolRx a few days ago, but still see the blue minerals are not completely dissolved. Why is that?

It could be due to flow over the unit. If you place it in your skimmer basket, but there was not strong suction, the minerals could take longer to dissolve. Also, in very rare cases, check the plastic outer shell. If the holes are not perforated all the way through on the top and bottom of Plastic outer shell, take a screwdriver and poke them through. This will allow the minerals to dissolve out easier. (This delay in dissolving completely does not affect the product, or longevity, it’s only a delay in seeing the results.)