I have a 125 gallon with an Fx6 and about 35 two inch Mbuna. Can't get my Nitrate under 40. Ph is 8. Ammonia is 0 Nitrite is 0. Tank had been running since Feb 6th. I do 30 gallon water change weekly and did first vacuum this weekend and will be doing weekly. Do I need a second filter or just keep up with water changes and vacuuming?