what air pump

[jonlpool]

i have a pond holding 10,000 litres approx, im after an air pump, any idea of what size i need and what type to go for, i have a hailea aco 328 , which i found incredibly noisey, so i have just switched it off... so idealy i want a quiet one... the pond is gravity fed from a bottom drain into a 2 chamber cloverleaf vortex and then media. The media is a bit sh*te and will change to kaldnes as soon as. So how many airstones will the pond need and the chamber?