We supply replacement tanks for most hydroponic systems. More popular now however are the flexible water tanks, made from a heavy duty reinforced pvc material, making them very tough. Moreover, they can be quickly assembled and disassembled, and are collapsible when not in use. This makes them easy to store or fit into areas that larger water tanks cannot fit into. Also, thanks to the zipper lid provided, the water stays clean and is easy to refill. If using a tank to mix and store nutrients, its important to remember. PH can change drastically in a few hours so check before applying to plants. Also, some of the nutrients (Not Hydro) are only designed to be used with in 2 or 3 days of mixing. Or else its money down the drain.