Current OHF has the following,

Im running it on a 5*2*2 tank which currently houses 3 aros, 3TFB and 2 plecos. Im thinking of getting a pair of rays thus the need for upgrading the number of trays but have no idea how many levels should I add and the media for them.
Any advise and suggestions bros ?
P.S. Black filter wool and black wool is the same stuff, typo*

Im running it on a 5*2*2 tank which currently houses 3 aros, 3TFB and 2 plecos. Im thinking of getting a pair of rays thus the need for upgrading the number of trays but have no idea how many levels should I add and the media for them.
Any advise and suggestions bros ?
P.S. Black filter wool and black wool is the same stuff, typo*