Mine's new so I don't need cleaning anytime soon... just wanting to know the right way. I've learned you don't want to kill the bacteria in the actual canister so what's the best method? I'm using an Ehiem that has 3 baskets. I'm under the impression when it's time to clean you should dump out the water, replace 1 or 2 trays with new media and leave the 3rd alone so you don't get rid of all the good bacteria. Is that correct?