I think all of these are oversized for your system in my opinion. I would look at the Alpha 170 for this size tank, or even a Bubble King Mini 200. The Mini 200 is a pretty big jump up in price though. Having said that, the ATB 840 was probably borderline for that size tank, depending on the load, the Alpha 170 would handle it with no problem at all, and you get quailty of construction that is unmatched! Warranty on the RD pump is 2 years, with a 10yr part replacement availability guarantee.