pulsing xenia

[golden69_ca]

dont get me wrong it is actually growing just not pulsing any more my kh is at 17 . i thought that was to high . i do a 20gal water change aprox every month . its a 90 gal tank . it has been up as a 90 for 2 months but the system was origionaly a 50gal that was up for 5 months . my tanks lighting is 2 4'vho and 4 4't3 actinics . they also prefer low flow ?

thanx for the help