how do i clean my external filter iv only cleaned me dads external pond filter and never cleaned my external aquarium before.i forget the brand doh .
what do i need to clean??how much etc????
and how often.
keep in mind they were houseing malawi's but now im moving to tangs in couple weeks.

Depends on the model.

Turn taps. Turn unit off. Remove taps/pump head. Take base to sink or wherever.

Floss needs to be changed ideally every 2 weeks, This may not always be the case as your obviously going to need to change it more frequently if you keep big or messy fish as opposed to neons.

Carbon if you use it needs to be changed every month, it only has a certain service life and after about 5-6 weeks it can begin to release what it has absorbed.

Sponge can be changed whenever they become heavily clogged. Most units have more than one so you can alternate the changing over several months.

Bio Balls/ceramic rings technicaly dont need to be changed to much however I'd change both at 6 month intervals just to replace the ones that have become clogged and cannot be cleaned.

Most importantly clean the impellor every time you open the unit. Cleaning the blades and the shaft will ensure you get the longest life possible out of it. However I'd even change this every year just to be on the safe side, for the few quid that they are, it'll do no harm.

Regards

ok cheers
but do i need to clean it fully out or leave some the mess there as cleaning fully
would ruin all bacteria etc

As long as you clean the media in TANK water, damage to beneficial bacteria colonies will be minimised.

cheers