Dear mds: although my daily diet is > 5000 mg of k rich food/fruits, my k is <3.4. by how much would 12.5 mg diuretic (hctz) decrease potassium level?

Can be significant: HCTZ (hydrochlorothiazide) can certainly do this! Also contributing can be subtle things like diuretic effects of alcohol or caffeine, even large amounts of licorice! Some forms of hypertension are associated with low K to begin with ("hyper aldosterone states") and are very sensitive to even low doses of HCTZ (hydrochlorothiazide).

Low potassium: Low potassium from 12.5 mg HCTZ (hydrochlorothiazide) is a surprise with a diet of more than 5 grams of potassium from food per day. Low potassium in you suggests an ongoing renal loss. It is essential that serum aldosterone be checked. High aldosterone can cause hi BP and low potassium that is very difficult to fix. Ask your doctor to check aldosterone; ask if you can switch to low dose spironolactone.