Catalyzes only the formation of fructose 6-phosphate by hydrolysis of fructose 1,6-bisphosphate. beta-D-fructose 1,6-bisphosphate + H2O = beta-D-fructose 6-phosphate + phosphate Binds 2 magnesium ions per subunit. Not inhibited by AMP and slightly innibited by hydrogen peroxyde. Optimum pH is 9. Activities at pH 8.0 and 9.5 were approx 67% and 85%, respectively, of that at pH 9.0. Carbohydrate biosynthesis; Calvin cycle. Homotetramer. Belongs to the FBPase class 1 family.