I am in the process of replacing the tanks on my salt water mixing station. I have noticed that many here are getting their tanks through places like Tank Depot, but the freight charges are often higher than the cost of the tanks. After some searching, I found this company and I couldn't believe they were offering free shipping (via UPS). It took 4 weeks for me to get the tanks, but the savings were substantial.
http://www.ruralking.com/ace-roto-mold-40-gallon-vertical-dome-top-tank-vt0040-18.html
THEY NO LONGER ARE ONLY ON THE 40 GALLON TANKS OR LESS! So I am going to go with 2 40-gallon tanks w/ Free shipping for my Mixing station..