Not that I have one, but this is what I have learned about the reactors:
Its usually recommend changing media when it either dwindles down to about 1/3 of the volume in the chamber or if when doing maintenance, the media feals like mud or mush. If when doing maintenanace it still feels "gritty" like it did when it was new, top off the media, if it feels like mud, replace 100%.
Hope this helps.........

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Richard
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My wife believed me when I told her it was only going to cost about $500.00. that was over two years ago and I'm still grounded.....