RO/DI and Automated Water Top-off for Reef Aquariums

A couple of months ago, I finally got tired of hauling 40 gallons of RO/DI water from the local fish store every two weeks. I decided the money invested in my own RO/DI unit would be worth the convenience. I shopped around and read reviews from other hobbyists and eventually decided on a custom 5 stage RO/DI unit from Aquatic Reef Systems. I’m glad I made the investment. Two of the biggest maintenance chores for my reef, topping off evaporated water and performing water changes, are now much easier. Here’s how I setup my top-off and water change system.

I ran the source and waste lines for the RO/DI unit out of a nearby window. The source is hooked up to a garden hose and the waste line drains onto the lawn. The output line is hooked up to one of two 30 gallon, FDA food graded, open head drums. One drum is used for top-off water and the other is used for mixing salt water. Both drums are equipped with a recirculating system powered by a Dolphin DP385 submersible pump. Most of the time, the water is pumped from the bottom of the drum to the top and constantly recirculated. However, by turning a ball valve, the water can be redirected out of the drum via a bulkhead and into the reef tank’s sump. This allows for quick fills of either salt or fresh water. The top-off drum is equipped with an auto top-off system that pumps fresh water into the sump as the sump water level lowers due to evaporation. This is a very convenient setup. To fill the drums, I insert the output line of the RO/DI unit into a speed fitting on whichever drum I want to fill. I turn on the water outside and let the drum fill. The drum is equipped with a float valve which shuts off water production from the RO/DI once a certain fill level is reached. The RO/DI water in the saltwater drum is salted to a salinity of 35ppt and heated to 82 degrees farenheit. The water in the top-off drum is buffered to a pH of 8.3 and left unsalted and unheated. Whenever I perform a water change, I remove about 25 gallons of water from the reef tank via an exhaust output on the main water distribution manifold for the tank and then flip a ball valve on the saltwater drum to add twenty five gallons of new saltwater back into the system. This setup makes top-offs and water changes quite simple. Here are some pictures.

This is the RO/DI unit. There are five stages on the unit: one sediment stage, one carbon stage, one RO stage, and two DI stages.

Here are the two drums. One holds freshwater and the other holds saltwater.

Here is an inside view of one of the drums as it is being filled. You can see the pump at the bottom which is connected via flexible tubing to a water distribution “T” made of CPVC. The water is pumped up into the tee and into the small length of flexible tubing connected to the left arm of the tee when recirculating. To send water through the bulkhead on the right arm of the tee, the left ball valve is closed and the right ball valve is opened. I could have used one three-way ball valve instead of two regular ball valves, but decent three way ball valves are expensive. It’s cheaper to use two ball valves, although not as convenient. The black block on the left is the float valve which shuts off the water. That’s a large Ebo-Jager heater dangling there at the bottom.

Here’s a closeup of the water distribution tee. Very simple.

Here’s a picture of the bulkhead. I put a ball valve here as well for added security.

Finally, here’s a picture of a drum that is almost filled. The fill line is several inches below the top of the drum. I lose volume but get peace of mind from keeping the water level below the bulkhead and the input. They are water-tight, but why tempt fate?

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