Wharf ?
Carbon does loose it's absorptive capacity after a few weeks, that is true. However its normally quite porous and will hold a reasonable amount of bacteria as well if left in place. So replace it periodically if you want to maintain the capacity to absorb dissolved organic compunds, chlorine, heavy metals, etc. If you're not fussed then you can just leave in as extra biological media. I'd only bother to remove it if it has a negative impact on flow rate through the filter, as o2 availability is probably more important than having extra media.
Why not just use the Fluval media in the Eheim ?
Is there any bio media in the fluval or is it just sponges?
If it is just sponges stuff a couple in the eheim along with some bio media, then after a month take the fluval sponges out and replace them with ones that fit properly
I am also under the impression that no ehaim ships with media included, so you gonna have to buy that as well
The media for the most part won't fit I think, sponges certainly. I've got a Fluval 206 and looking to replace it with the below. It comes with media as far as I can tell.
https://www.eheim.com/en_GB/products/technology/external-filters/ecco-pro-200
I suppose I could move the Biomax but not sure on sponges since I'd need to cut them up. Some have suggested putting the old ones directly in the tank but not sure if this is good advice or not. I don't have much choice but to run a new filter without running it in first, so want to ensure I take any precautions I can. What do you think?
Yes move the biomax over (All of it) sponges are mainly mechanical filtration anyway.
The biomax is most important.
leave the sponges out of your new eheim when you get it and use the biomax instead, after a month (when the new bio-media has established) you can remove your biomax and put the sponges in.
You might not get great mechanical filtration during this period but without a 2nd filter to backup your new one I don't see another way of doing it
Also, it says the phosphate pad should be replaced. Like the carbon, is that a grey area, too?
Unless you actually have issues with phosphate levels etc then there is no real need for such products, as long as you keep on top of general maintanance.
If your tap water has high levels of nitrates, phosphates etc, then they can be useful as there isn't a great deal else you an do but purify it after it's come out of your tap.
If the pad is already in your filter, let it run its course and then remove it. They load up on the absorbed phosphates and eventually get "full" and won't absorb any more.
With chemical filtration, there is a chance the impurities will gradually leach back in to the tank if the pads are left.
I've kept fish for over 20 years and in general I use fine poly-wool for "polishing" the water (trapping finer particles suspended in the water,) the sponge pads for mechanical and biological filtration and the loose rubble/noodles for biological.
Fortunately I've not had any real need for chemical removal pads etc.