Ammonia that remains in the blood even after filtration is actively transported into the nephronal fluid. Some ions are actively transported out of the blood. E. Artificail kidneys and dialysis . The adrenal cortex does the ion detection directly. Note that this also affects water uptake.
Less aldosterone can mean more dilute urine.
Note that this can also affect blood pressure. Less aldosterone can mean more water water loss and and less salty medulla which reduces the pressure of water reentering the kidney capillary system. Angiotensin II stimulates aldosterone secretion. The filtration rate is constant, therefore there is no control elicited here. Passive reabsorption due to osmotic pressure from proteins in the blood.