Everyone will have a different schedule for changing their phosphate remover, and as lando mentioned it completely depends on the amount of PO4
that is being introduced.
Theoretically, if you are keepong your introduced PO4
's down, then every 6 months shouldn't be a problem. I wouldn;t go any longer than that, but it can be stretched to that in some circumstances.
Personally, I think every 2 months is a waste of money unless PO4
is a huge issue, and in that case some PO4
detective work is in order to cut it out at the source.
You also have to look at the media you are using, some will start to leach back into the water when it becomes spent, some claims it won't leach but still will slightly, and some won't leach at all, it will just stop removing it.
If you regularly test your PO4
, you will be tipped off when your readings start climbing but your routine has stayed the same..... at that point, change the media. That's the best way to get full life out of your media, but it's more work than just putting it on a 4 month schedule, for example.