Petco is having a 4th of July blowout sale (valid now). Everything is 20% off, no coupon code needed.
In addition, they are running their ever famous $1 per gallon sale on aquariums. All aquariums 55 gallons and under are $1/gallon. The 40 Breeder is the best value here as it's usually ~$110. For proof of this sale, scroll to the bottom and click on "local ad" and then type in your zip. It should pull up your ad and have it in there. Mine was on page 4.