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That's not an easy answer. Different carbons last different amounts of time. Better carbon is usually depleted in around 2 weeks from what I have read. I wouldn't worry about it too much. Turtles aren't like fish that need a lot chlorine removed. I would say fluval brand is probably a high quality carbon. Some people don't use any carbon! I like to use it myself. Keeps my tank nice and clean... I also use purigen but that's a whole other story. Do some research on carbon in turtle or fish tanks and draw your own conclusion. There is a lot to learn about carbon and its uses.

ive had this carbon for like, months O_O oookay.. i shall get new carbon and load uf my 406 i know i saw this before... but what are the ill efects of chlorine in a turtles water?

If I'm not mistaken its eye irritation and skin irritation. Like I said some people don't even use it but carbon also helps with smell and keeps water crystal clear.

k