i started with about 1o in a 2ft tank with terrible bba , only now that there is (at a guess) close to 100 is the algae controlled
shrimp are good algae eaters only effective really when in large numbers and not able to feed on fish food
if used with a normal tank then i doubt they would make a hugh difference , for plants i would suggest movbing badly affected plants to the shrimp tank for cleannig then return to normal tank once recoverd
as with anything stocking rules(of thumb) are purely rough guides, as long as water quality is maintained then shrimp ccan be crowded in
andrew