I only know of two products that can boost blues.. both are ZEOvit additives. One is Potassium Iodide Fluoride and the other is Jodi Complex. I believe it's actually the Iodide that does it and not the potassium part. To much Iodide can darken other corals so be careful. Iodide comes in different forms (iodate, iodide and others) I couldn't tell you the differences just that the ZEOvit Jodi Complex is a blending of them.
Potassium Chloride would boost the K levels but may have little effect on blues. It may brighten corals in general if the K level is low. Most salts are adequate with K levels, only bacterial systems may need supplementation due to the increased anaerobic activity.