I think I will dose bio spira, wait a couple days and dose eco balance. Thanks for the input!
Have you considered replacing the MarinePure with a loose (passive flow) sponge? This would serve the same purpose as the ceramic medium without the crumbling (I've sold a lot of that stuff and know exactly what you're talking about). I think both fishface and Spare Time are correct in that there definitely are some small number of nitrifying bacteria on the outside (i.e. aerobic) surfaces of the medium, though the majority of the inner surfaces (most of the block) are likely colonized by anaerobic (e.g. denitrifying) microbes. Thus, while you might not experience a substantial spike in NH4/NO2 after removing the MarinePure from this type of application, you could actually see elevated NO3 concentrations a bit further down the road. This is why I'd recommend an anaerobe such as R. palustris (PNS ProBio) that assimilates NH4, NO2 and especially NO3. I've soaked ProBio directly into a sponge and used this as the sole source of filtration in a newly set up and heavily fed NPS system--never had any sort of nitrogen cycling issues, even with minimal water exchange.
On the NPS system, do you do water changes or run anything else? I have not personally used PNS probio but I list that as one of the good biodiversity products out there when people ask. I was thinking of getting some just for the heck of it.