K1 kaldness sump question

[hansoloNZ]

Hi all. I'm setting up a large sump for my 250litre. I'm wondering if 1 large compartment in the middle with K1 moving bed will be better than several compartments with various different media (Lava Rock, K1, Bioballs)? Thanks heaps!

 

[wkscott]

Don't know about the sump itself but you don't want lava rock in it. Lava rock is primarily made of silicates which will constantly leach into the water. You will have massive, endless diatom blooms. In addition the rock could contain any number of toxic heavy metals that will react with seawater.
You also won't want the bioballs. Although effective at removing ammonia and nitrite from fish only systems, they do nothing to remove the resulting nitrates. High nitrates can be harmful to fish and even worse for corals and other invertebrates.