Little bit more info:
Tank - 55L(14 Gallon) - Aqua One 150w Heater, Aqua One Aquaris 700 Canister Filter
All stats good, tested at fish shop.
Fish: 2 x adult male - 2 x adult female, 2 x teenage female, 1 x Baby female, 1 x bristlenose about 3 inch long.
30% water change performed 3 days ago...