It depends on usage and how much dirt it absorbs.
But I'm going for regeneration every 3 months.
You use bleach to clear it up, then seachem prime to make it safe for reuse.
I've never regenerated before, will do it in the coming weeks, I can post some info on how it went,
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300 - 400ml bag, how big is your tank?
And it's as easy as that?!
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You can't beat a diatomaceous earth filter for crystal clear water.