Fresh/Saltwater Storage


I have a 4-stage RO/DI system that I use to make my freshwater. I mounted the unit in a rubbermaid container so that I can store it on the back porch. When I need water, I hook it up and turn it on. The RO/DI then fills a 55 gallon container. This container is plumbed to another  gallon container that I can use for making up my salt water. The containers are stored out of the way on the back porch, but close enough that I can run a hose from the saltwater container to the tank  through one of the windows. This makes water changes super simple.


The first part of building this setup was mounting the RO/DI unit into the storage unit. I also ended up adding a pressure pump. I wanted to control when the pump was on manually, so I put a switch on the outlet that it runs on. The storage unit runs double duty for the control system for my pool cleaner.


Once the RO/DI unit was safely mounted, I built a platform for the storage units to sit on. The platform is made up of 2x6s and a 1/2″ OSB top. I coated all the wood with two thick coats of outdoor grade primer.


Finally I plumbed up all the storage units. The first time around I ended up with leaks, so I had to redo it. The second time, I used plumbing paste to help seal the threads. I also ended up buying a bung wrench to make sure they were on good and tight. Now there’s no more leaks.


The storage containers from left to right are Freshwater, Saltwater, and 2 waste water containers. The waste water will be used around the yard or for filling the swimming pool when it gets low. The Freshwater and Saltwater containers have a 4″ threaded clean-out mounted to the top of them. This is so I can rinse them out from the top if needed. The one on the Saltwater storage serves double duty as that’s where I’ll be able to add the salt. There’s a Mag 9.5 pump mounted between these two containers to help with moving water from the fresh side to the salt side and to help mix the salt water. The pump is rated at over 900 GPH at 0 head, so it shouldn’t take it but an hour or two to completely mix a batch of salt water.

My only concern with this being outside is the temperature swings throughout the year. I’m considering mounting an Arduino nano out there with a temp probe and heaters to keep the containers from freezing. I can also run a button to it so that it can raise the temperature of the salt water storage up to match the aquarium prior to water changes. I’ll wait until the end of the winter season to see if it’s really needed or not.


Performing a water change is quick and easy with this setup is pretty quick. I use the top-off controller to automatically turn on the pump outside to pump fresh salt-water into the tank as the main pump pumps old water out of the tank. I made a quick video of the process. The entire video is 6 minutes, which is about the same amount of time the actual process takes start to finish.

As mentioned in the video, the water temp did drop during the process, but it was less than 1 degree as can be seen in the following image.