When is a good time to change media in a calcium reactor? I had Bob's MRC2 dual chamber and it was full when I bought it, but I have had the same media in it for about 6 months. One chamber is a little over 3/4 full and the other is just under 3/4. I just am not sure if the media loses it's effect after so long. I still am getting good growth, but would like to be a little proactive instead of reactive.