First post, need a little help verifying my math on sump tank

[TwistedMind]

So, i got a second 75 gallon tank for free. 75 gallon display, 75 gallon sump anyone? Seems like a waste to me but I might make it work if I can't find a 40 breeder for cheap pretty soon.

[reefreak]

usually petco has $1 to gallon sales you might want to check there