Do NOT drain a crystal clear pool!

If it's not broken, don't fix it!

You can do a 50:50 dilution with tap water for the CYA test, but not for any other test. For pH, TA, CH . . . you must dilute with DISTILLED water, which Walmart sells in gallon jugs for about a dollar.

Diluting for the pH test with distilled does NOT change the pH -- so there's no multiplier. It's just a way to get fairly accurate pH result when the chlorine is above 10 -15 ppm.

ABSOLUTELY, test your fill water BEFORE you even consider draining and refilling.

Once you have those results, you can think about options.