75 will be good enough, like Zorro i had a breeding pr in my 55 but was much happier whe i ave to a friend wit a 75. Male got to 13 and female 11, then the damn storm hit and now we trying to find some more.
I was about to get a 100+g and try to introduce another female for higher production. The biggest batch was 200 so i hope you have a good G.O. tank(s)