I have canister filters on my three largest tank, two are Eheim Pro II (in continuous operation since 1996) and one is a newer Rena Filstar 3. The frequency of cleaning somewhat depends upon the aquarium. I need to do my 115g with the Rena every month or at most two months or it does become noticeably slower, whereas the other two can go three or four months. But I have fairly heavily planted tanks so my filters are primarily used to circulate water and remove suspended sediment, and less for biological filtration.
Having said that, it is best to get into a routine, such as every month or every second month or perhaps every third month. Not knowing your tank size, fish stocking, plants, etc, I have to be very general. The water must contiinue to flow basically unimpeded through the media and pads.
As for cleaning it, I always clean mine under the tap. Once your tank is established, there will be nitrifying bacteria everywhere, not just in the filter. If you have live plants, even better. But using a bucket or two of tank water won't hurt if it gives you peace of mind, and in a newer tank or one without plants, I would use tank water for a while.
The pads can be rinsed. The blue coarse pad (I have this in my Eheims too) will last almost indefinitely. The white fine pad I replace when I clean the filter; I used to rinse this out too, but I found that it lost its shape and wasn't giving the best fit, and if water can escape around these they are next to useless, so replacing the fine pad at each cleaning works well. The hard media you can just swish around in a pail; the ceramic disks last forever and never need replacing. The bio media Ehfisubstrat I never replace, again because biological filtration is not necessary with plants, but Eheim recommend this be regularly replaced. Some will suggest replacing half at a time, which is fine if you have it separated into two baskets, but if not, there is no way you can keep it separated so I would just replace all of it if you do this. However, this again depends upon your set-up; without live plants when this is your major biological filtration, you need to do things more slowly.
Byron.
an
