po4 levels reasonable fluctuation killing algae

Hi: We have been using the Hanna Phosphate Checker on our two tanks. Our 32 G is 0.043 ppm and our 16 G tank is at 0.034 ppm. I know the recommended level is less than 0.03 ppm. I am curious as to what type of fluctuation long time reefers see in their phosphate levels? As or 32G was...