You want about 5 to 7 x the main tank fro flow rate. 70g = 350gph to 490gph.
When you size the pump add up the head (height) from the pump to the highest point on the return line. Add 1ft for every 90deg bend and make sure the pump you purchase can meet the flow requirements.
When you size the pump add up the head (height) from the pump to the highest point on the return line. Add 1ft for every 90deg bend and make sure the pump you purchase can meet the flow requirements.