Is it possible that , in a good working canister/filter , there is a release of Nh4 in that amount that it can induse algae? For example my filter isn't cleaned in 6 month, i've got no reduction of flow from the outlet and no no2.
At what termine do we need to clean our filters(extern).

It's more than NH4 that seems to cause algae, any type of excessive organic buildup can contribute. So if your filter is clogged with dead/rotting debris, that can easily contribute to algae problems whether or not NH4 is being created directly. How quickly it gets substantial organic buildup depends on a lot of other things.

I think that each and every filter associated with an individuals tank is going to require its own cleaning schedule based on all of the variables involved in aquaculture.

Start by checking every two weeks, if clean then once a month, if clean then once every two,three,six, months ... :-))

Thats the idea.

If you have a planted tank then I would problably not worry about Ammonium (NH4) released from your filter as It is often prefered by many plant species to NO3 as a source of N uptake. But if you have no plants then you should clean the filter before six months to prevent algae.

Drain some tank water into a plastic tub/bucket/pan that you use only for tank maintenance and pull the floss out and gentle shake and agitate it to release the larger particles and put it right back into the canister if you rather not put in fresh floss.

I don't think any denitrification is happening in a standard filter. You need a special type of anaerobic filter to accomplish this. If you're talking about nitrification, once a tank is well established, rinsing the filter media gently shouldn't harm it.

sorry i meant nitrification.

Rinsing the media in tank water won't harm the bacteria much, all you're doing is trying to get solid waste out of it. Just don't go wringing it out or anything. Plants themselves have lots of bacteria growing on them so any decrease in your bacteria in the filter can easily be compensated for in a planted tank, if it's well established.