I just finished my sump made with a 40 gallon breeder tank and my setup is very similar to yours. My baffles are 8" high for the bubble trap and 12" for the refugium. I was going to put a deep sand bed and live rock with cheto, which is what I have in my current tank. I have not heard about choosing between sand or cheto and not using live rock in a refugium. The main reason for my refugium is to grow pods for my tank and nutrient export via the cheto. What am I missing?
You won't be hearing it a lot, till it becomes less of a fad to toss everything in the sump, because growing pods is good. But then if your system is running and well managed, pods are growing in the main tank. So one would ask then what is the point of growing them in the "fuge," when the object of a sump is export. Pretty much a universal notion, as "and export" is usually in most folks "excuses."
What function will rock rubble or other "live" rock perform in the sump? Bio balls have one purpose: a substrate for colonization of nitrifying bacteria. Such objects are scorned in the hobby today, as being "nitrate factories," which they are. But we don't want that do we. So we toss rock in the sump instead, which is strictly a substrate for the colonization of nitrifying bacteria. (Just the same as it is in the main tank--except you can stick corals to it and make an aquascape with it.) If you really look at it, it is completely pointless to put rock in the sump. We want to get rid of nitrate, not produce it, right?
Sand is a very effective substrate for the reduction of nitrate to nitrogen gas. But the use of it, if you do not want it to turn into a garbage dump, is rather strict. In terms of flow rate (SPS flow rates to prevent detritus fall out.) Chaeto (more appropriately macro algae, as Chaetomorpha is just one of many) utilizes nitrates. So they are both "export" methods, that are somewhat redundant if used together, although the sand is much more efficient--if done right. So if you use sand, the right way, macro is pointless--and there is not any room for it (or rock) anyway. If you use macro, then that violates one of the provisos for an RDSB, which is nothing else in it but sand and water. All very long, mostly circular arguments.
Many are in a "pod" mania these days, however too many cannot deal with the dissolved organics already present, let alone adding more bio load by intent, which simply increases the burden on the rest of the system.
Only one method deals with the full cycle, dissolved organics > free Nitrogen: the DSB. So what is more advantageous to the system? Growing pods? Or dealing with the real problem in marine systems: dissolved organics? If you want to grow food, start a phytoplankton culture, but oops it takes some copper......
ah, but if we call the slow flow fuge a detritus settling zone does that make it better? having a single garbage dump makes it easy to clean, but I guess one does need to clean it. It certainty is better than running dirty socks that accelerates the organic absorption.
the real question might be is how slow the flow need to be to qualify as an engineered garbage dump.
A circular argument. Collection of detritus, whether it be in a sock, or settling area produces the same results: Higher levels of dissolved organics, heavier bio-load, heavier burden on the system. One would be more inclined to replace a sock, than clean out their fuge, and--they don't clean the socks often enough: everyday.
