IIRC they run the 50% off sale every one or two months.
They had a glitch on Sunday where 2.5-gallons were $3, 5.5-gallons were $4, and all 20-gallons were $11. Lasted for hours, and all the stores near me sold out before I could get my hands on a few- which was a real pity, as I had wanted more smaller tanks for rearing fry.
I have been told that Petco is trying to phase out Aqueon products for their Imagitarium brand-based products, but I have no idea how true that is.
All I know is that if they stop selling cheap Aqueon tanks, I have no further need to shop at that store.