hey yetdrvr,,,i have my 180g tank right by the wall and obove basement,,,with the same floor joint like your,,but my house is 1999 builded,,and the older house i think there wood much harder so if you look around the joist and floor above ,,not thing like rot or moiseter then go for it,,,i don't jack my floor up,,and i have 180g with another 100g 10feet away,,,no problem here,,,as long at the joise is solid wood of 2x6x12max,,,then you can go to 220 no problem,,
i will replace 180 with 220 same place,,,very soon if you want to see picture i will get you some,,,good luck,,