Two tanks both with external filters.
120 litre tank has gravel but only small fish so vacuum gravel rarely at the moment (totally cleaned just eight weeks ago so there is nothing much to clean).
240 litre tank has sand. I have started on a program of taking a section of the tank and then using a hosepipe, I start to siphon the water into a large bucket outside near the drain. Once the water is running strongly I start to dip the end of the hose into the sand. This obviously sucks up the sand [BEWARE BURIED KULHI LOACHES (no, I haven't sucked any up)], takes it through the hose and into the bucket . The bucket can fill up and overflow into the drain leaving the sand in the bottom. Every now and again I stop, stir up the water and pour off the detritus then carry on. After I've finished, I use a plastic beaker to put the sand back into the tank at the back so the fish can spend their days moving it to the front again!!
. This method cleans the sand, removes any methane bubbles and generally tarts things up.
In both tanks I change about 35% of my water each week with an extra change midweek to the large tank ('cos I have large fish in it) of about 15%.
I used to clean my filters every couple of weeks but realised quite quickly that I was wasting my time so I intend to leave them until the flow drops off a little before interfering or every six weeks or so whichever is the sooner.
I was reading about Hamburger Mattenfilter (
See Here) and learned that bacteria perform better with a slower flowrate. The Mattenfilter are not changed or cleaned for up to two years and are expected to go brown as that is the bacteria so I thought why am I cleaning my filter material so often, so I stopped. So far, so good.