Backyard Aquaponics
A place to discuss aquaponics

Stratification is when the dense cold water settles to the bottom, and warmer less dense water sits on top, as happens in slow moving rivers and farm dams. It means there is a large temperature gradient between the warm top water and cold bottom water. This is bad for fish, who dont like sudden temperature changes. The warmer top layers are also relatively deficient in dissolved Oxygen, as O2 is less soluble at high water temperatures. You need enough water movement throughout the entire tank to prevent it.

Sumps are not absolutely necessary, but are great for adding water and stuff like KOH or Seasol, which the fish may not appreciate being added directly to the FT. It's best to have any additives thoroughly mixed and diluted before they enter the FT. They provide a bit extra thermal stability to a system too, due to the greater mass of water, and give you a bit more leeway for evaporation if you make them a bit larger than the absolute minimum required.