Spiro definitely lowers blood pressure, and requires a change in sodium intake if your BP was already a little on the low normal side.
I monitored my BP twice daily and was controlling it by restricting sodium, typically 700 mg/day. I use diet tracking software (MyFitnessPal) to log everything. Everything! Yeah, OCD much?
On spiro, I saw an immediate dip from numbers around 110/70 to more like 85/60 to 95/65. I uppers my sodium intake to about 1500 mg/day, and the pressure has come up a bit. I was slowly ramping up my daily spiro dose to the target the endocrinologist had recommended, while tweaking my sodium intake. Oh, the joy of being able to eat a bagel after all these years!
(I've had to stop HRT, alas. The prolactin numbers were too high. That's another issue, though.)
I suggest tracking your sodium closely, along with liquid consumption and BP, until you settle into a 'new groove'.