Nitrates still high

Hey guys,



So my tank has been curing now for 3 months and I still can't get my nitrates right.



pH - 8.2

Ammonia - 0ppm

Nitrite - 0ppm

Nitrate - 5.0 - 10ppm



What's going on?!? I feel like my tank should be cured by now. I do seem to be having a lot of brown algae. I am doing water changes weekly 10-20% of the tank.



So advice would be greatly appreciated!



Thanks