Thank you
I dont know how often I need to clean it as it's working second dayyes
it's undergrawel filter but conected to external filter 1000l with 9w UV lightplus booster
for better filtration and more space for good bacteria growing. The problem was with sediment on top layer of water. All filters for aquarium have that floater what collecting as well top layer but it need to be deep water to work well. I did put 3cmx3cm china water pump 1cm below the water level to pump all sediment under the undergrawel filter if I want to clean top of it and it's working well.