Generally you should rebuild your pond aerator compressor unit every 3-5 years under normal conditions.  Air filters should be changed or cleaned once or twice a year. 

Pond Aeration Rebuild Kits & Filters

SRC Stratus Compressor Rebuild Kits Fits Gast
SRC Stratus Compressor Rebuild Kits Fits Gast
$65.59
Stratus SRC rocking piston compressors contain these wearable internal components. Like tires on your car, these parts need...
DC22, DC12, Repair Kits
DC22, DC12, Repair Kits
$75.29
DC22, DC12  Repair Kits If your air compressor runs but does not pump air after a couple years...
ERP Compressor Rebuild Kits for EasyPro Stratus Aerators
ERP Compressor Rebuild Kits for EasyPro Stratus Aerators
$57.99
ERP rocking piston compressors contain these wearable internal components. Like tires on your car, these parts need to...
Vane Repair Kits - RV33, RV75, RV100 Gast Compressors
Vane Repair Kits - RV33, RV75, RV100 Gast Compressors
$109.89
Rotary vane compressors each have four self-wearing vanes, when worn they no longer catch air resulting in reduction...
SRC Stratus Compressor Rebuild Kits Fits Gast
SRC Stratus Compressor Rebuild Kits Fits Gast
$74.29
DC22, DC12, Repair Kits
DC22, DC12, Repair Kits
$79.39
ERP Compressor Rebuild Kits for EasyPro Stratus Aerators
ERP Compressor Rebuild Kits for EasyPro Stratus Aerators
$57.99
Vane Repair Kits - RV33, RV75, RV100 Gast Compressors
Vane Repair Kits - RV33, RV75, RV100 Gast Compressors
$109.89