I find after about a year enough of the media has broken down to the point that it works its way into each other. So the "feel" of it and the "look" of it hasn't much changed, but the pump has to work a lot harder to push water through that, and that seems to create secondary "issues", such as blockages (pressure building up in some areas, possibly leading to leaks).
Anyhow so far I've found it best to change the media out, outright, sometime after a year's worth of use, rather than just keep topping it up indefinitely. Other people may have other experiences though.
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-- Tony
My next hobby will be flooding my basement while repeatedly banging my head against a brick wall and tearing up $100 bills. Whee!
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