It is a RO bladder tank off of the RO only part of the RODI. the output of it goes to the water dispenser and ice maker in the refrigerator. That in not aquarium related but turning it on every 4 hours for 15 minutes keeps the pressure up enough for the usage it gets. Mostly ice since we usually drink bottled water. Our water comes from a lake and during certain times of the year the ice will have a bad smell to it if we just use tap water for the ice maker. The RO unit removes the smell. There are some other non aquarium things I use the Hydros for since I have it and it can do it without any trouble.Why do you have an ice bladder?