How to replace carbon (GAC) in a Phosban Reactor

To maintain crystal clear water quality, I find that it is essential to use granulated activated carbon (GAC) in my system. GAC is sold everywhere, and brand names are often compared. The key to picking out a good carbon is one that doesn't release a lot of dust into the tank and doesn't contain any trapped phosphates. I've seen many sumps that contain a mesh bag (or a nylon stocking) packed full of carbon, which the hobbyist believed would help water quality. This is called passive filtration, and it is an inefficient way to utilize carbon. Over time, a film or skin develops over the mesh material and water simply passes over and around it instead of flowing through it. Instead, I opt to put GAC in a Phosban Reactor (made by Two Little Fishies), where water is pumped through the media. This is called active filtration, and what I recommend to everyone.

The Phosban Reactor 150 can hold up to 3 cups of carbon. The unit costs less than $40, has an easy-to-unscrew lid, rubber connections, and is simple to clean. It is about 3" in diameter, so it takes up little space in a sump, and can even be hung on the back of a display tank if no sump is used. Half a cup of carbon for every 50-gallons of water is what is recommended, but opinions vary on how long it lasts. I believe it is only good for a few days, personally. Once it has done its job, it would be best to take it offline before it becomes a nitrate bed. My routine is to change it out every two weeks, as my mixed reef definitely contains a lot of chemical warfare between the varied corals.

First, I disconnect it from its pump in the sump, and set the reactor in the sink. I love the Phosban Reactor's rubber connections, which are simple to press in or disconnect.


After removing the lid and draining all the saltwater into the sink, I'll dump out the old carbon into the trash, then clean all the parts with tap water. A pipe/tube brush works great to clean out the riser tube sections.




These are the basic items I use. Carbon, a canning funnel (sold near where you can find stuff to make your own jelly preserves), and some carbon. I bought a large amount in bulk years ago, and bagged it up in separate one gallon bags to keep the majority nice and dry. A single bag will refill my reactor four or five times.




Using the other end of the pipe brush, I press the mesh pad down on top of the perforated red plate in the reactor. The wooden spoon handle would do this as well.




The funnel is then placed on the reactor, and the wooden spoon handle is inserted into the riser tube to keep the carbon out.





Add carbon. My reef may or may not need this much, but usually I use between two and three cups of carbon. The reactor holds three cups, max.




Next, the mesh pad is placed around the riser tube near the top.




Then the second red perforated plate is installed. This will keep the carbon in place during the rinse. Fill the reactor with RO/DI water.





Placing my finger tip on the riser tube to hold everything in place, I'll pour out all the water and any carbon dust.





After it is poured out, I refill it with more RO/DI water, hold the center tube firmly to avoid dumping out the core with all the carbon, and pour it out again.






Finally, I refill it with RO/DI water to the top. This keeps the reactor from floating or bobbing in the sump when I hang it in place.


The lid is screwed on.


And lastly, reconnect it to its pump in the sump.



I have it set up with the output pouring quietly over the Mag 7 -- my calcium reactor's circulation pump, effectively cooling it as it pours into the sump's return zone.

The carbon is changed out every two weeks. If the water starts to have a green tinge to it, it's time to swap it out.