How do I know when I need to replace the charcoal in my aquarium filter?

Question

I recently purchased and installed an External Canister Filter in my aquarium which includes a filter stage with little bags of charcoal media.

Clearly I need to replace this at some interval because the manual tells you how to replace it and I see them selling it at the store, but the manual says nothing about the frequency or determining when the charcoal media needs to be replaced. I'm assuming I don't wait until it is gone, but does it change color or something to indicate it is used up? Will my tank start getting more algae when it stops working? Can I tell by smelling it? Or do you just have to do it at a specific time interval? If so, how do I know what that time interval should be.

Answer 1

The usefulness of carbon in your tank is, well, debatable... there are some pros and cons, some not always grounded in good science.

Anyways, the useful life of the carbon portion of the filter is about two weeks and it's good for removing any contaminants or medications you may have needed to add to the system in that time. Beyond that, the filter is less useful. What you want to make sure is that when you're changing your filtration, you don't remove the bacteria (or minimize it) that are actually working to keep the tank, and your fish, healthy. What will keep your system in good shape is proper water maintenance and so you might want to read up on the nitrogen cycle as a way of keeping your scaly friends healthy.

Answer 2

Yes, you´ll need to replace it, but only if it is saturated and you need to remove chemical components from your water. And it won´t change it´s color, nor have a specific smell (unless you´re having a hard time on your aquarium, it´ll have the same smell of the water and everything else).

Charcoal (activated carbon) is used because it absorbs chemical components, filtering them. For example, if you have used some medicine in your aquarium, this charcoal will be responsible for extracting it from the water.

Some argue that this filter isn´t necessary in your aquarium, since you´re not adding chemicals to it all the time. In that case, you would use it after using some products in your water, and it´ll be "filled" in about 2 weeks, and beyond that it looses it´s filtration property.

It might work as a bacteria habitat, in the famous nitrogen cycle, so leaving it could make no damage. And then you should never replace all the filtration elements of your aquarium at the same time, because you´d stall your nitrogen cycle and would have to begin it all over.

In your case, specially because it´s brand new and is already in use, I´d leave it there, and would just change if some chemical product was used. You would be filled with bacterias, the product would make it´s effect, and after this "while the effect must be produce time", I´d replace it to take the leftovers from the water.