My flow rate would definitely be on the low side and if you have or seen a TLF150 the diameter is very small, however since this issue I also follow the KZ recomendation of soaking carbon in 90 DegC RO for a 24hr period prior to use (I just put some RO in the mircowaver and boil it then soak the carbon in it). I assume the high temp helps to release something maybe in the carbon. The Rowacarbon is quite clean though and generally one rinse would take out any fines.
So I still use it, always have, however am cautious as I had thought you could of never overdose carbon. As I think about the usage, with rowphos you need such a little flow and it removes PO4 so maybe the flow rate through the carbon (if we primarily use it to remove toxins) does not need to be very much. When setting my flow I have only ever set it so I can just see a few grains just moving on the top surface. I know some people set it up like the top surface is boiling...as they are scared it will solidify, I have never had that problem with rowaphos or rowacarbon even with very low flow rates.
With all this talk of "passive" maybe Ill just get a long sock and hang the carbon in the sump and give it a tumble twice a week just to be on the safe side.