I have a c-530 on my 120. Has lots of space for filter media. But I want to try an FX5 here pretty soon cause I need more bio for the fish are getting bigger.
FX-5 is good but cant say the same for your fish stocking. No way a 125 is ok for an arowana. The 2 O's are going to harass that Aro to no end untill it gets bigger than them but then as I said a 125 is not a good tank at all for a silver arowana.