Who out there uses K1 in their sump?

I'm hoping to get some info from your experience with K1 in sumps. I've just purchased a whack of it used (I think 85L). Tank is 300g, will be African peacocks/haps, sump will be 75g. Trying to get a feel for how much K1 media to use as I am designing the sump. I like the idea of overkill but then there is OVERKILL! I think I can fit 50L in the sump if I have nothing else other than narrow inlet area for some mechanical filtration and narrow area for the return pump (and I've got to fit in 3 x 300W heaters somehow). I am unsure if I should use all available space for K1 or if I should make compartments 1 & 3 abit roomier or even a small compartment where I could put in bagged media for whatever reason I may have (no intentions at this point).

Thanks.

I still don't know if my heaters (3x300w ebo jagers) will fit into my anticipated pump chamber. They will need to be on a front to back angle that is for sure. Unless I fit them under the K1 chamber and have some sort of mesh/screen divider to separate the heaters sitting on the bottom with the K1 above. Not sure how that would work? May need to modify the dimensions but will due trial run before siliconing anything! Was hoping soupa2 you would figure it out first