I wouldnt mix bluelegs with scarlets, i woudnt get bluelegs in the first place. I started with 20 scarlets and 10 bluelegs. 4 months later i have 3 scarlets(the biggest ones that i had) and 7 bluelegs. I dont believe that having extra shells will help any because if you do the math, i started with 30 and now have 10, that means 20 extra shells in the tank somewhere, yet even tonight i saw 2 blue legs fighting it out. Bluelegs look nice, but are over aggressive. Scarlets look nice but seem to be lazy to me. I like the baha red legs i have in my 10 gal, they are constantly active. JMO