2-3 35% water changes with raking sand substrate and rinsing all large ornaments with siphoned tank water. I do this because the tank is 180 gallons with 26 small to large (9" fish) and 5 plecos, 3 sailfin and 2 bristlenose.
My bio-load is very heavy and with white sand as substrate you can see every bit of waste in that tank. The tank was also recently set up so its still needs to purge that last like 0.00005ppm of ammonia or maybe its just the huge bio load because its been 2 months and i still can't get the ammonia tester to turn completly bright yellow, always a tinge of light green which indicates .25ppm of ammonia on my color chart but its never all the way so its somewhere between 0.0ppm and .20 i believe,
anyway i do a lot of water changes and i do them 5 gallon bucket at a time for a 180 gallon tank, but each 5 gallons is delicately treated and brought to exact aquarium temprature, which may sound like overkill but you should see the fish when i pour the new water in, the bathe under like a water fall and seem to love it.