if you believe anything that Dr. S has said, and especially what was linked to earlier in this thread, then i am sure i am going to ruffle some feathers.
refugiums, lets call them live sumps, do not work as advertised. they are just glorified cesspools. the object of them is to allow detritus to collect in a certain area, a noble goal, then let the detritus rot in order to support an organism that we do not want in our systems anyway in a odd belief that it is exporting nutrients in a reasonable manner, which they are not. they are after the fact nutrient removers and do not go after the source of the nutrients. live sumps, GFO, Chaeto, ATS's, they are all after the fact nutrient binders. they are only able to bind nutrients after they have been released from detritus by bacteria. extra steps needed.
here is a nice chart showing the different ways to export nutrients from our systems.
as you can see going after the nutrients after they have been incorporated into algae is not very effective at lowering the nutrients out of system.
the only reason to have a substrate in a live sump is to bind phosphates. that is what calcium carbonate does best. it is this fact that has been ignored by Dr. S and others who promote the use of substrates a complete filter for our systems. this is not correct. calcium carbonate is a fantastic phosphate binder just like GFO or Aluminum Oxide. how can something that does this be expected to last indefinitely in our systems? it can not. it does last indefinitely in nature either. it needs to be cleaned and reset in order for the phosphate engine to keep working. problems occur when the phosphate engine is clogged by detritus. there is not a mechanism for migrating phosphates out of substrate besides manual removal. this is what has been ignored in this hobby since the start of the DSB craze where we were told not to touch a substrate. if the substrate is working properly, then why would we need to touch it? why does one have to remove substrates slowly if they are processing nutrients so well? why does old tank syndrome look and sound exactly like eutrophication on natural reefs? if H2S is caused by nutrients in an anoxic area, then how did the nutrients get there if the substrate is being cleaned all of the time by magic worms? do the magic worms send the detritus to another dimension?
i am not saying do not use sand in system or in a live sump. i am not saying not to use a true refugium (a separate body of water of the same trophic level that keeps an organisms safe from predation). what irks me is that live sumps are recommended for everything without actually understanding exactly how they function. i am a firm believer in using an area for collecting detritus in an easy to siphon location. the lower the flow the better. i just do not believe in keeping this poo as a pet in order to provide the nutrients needed to fuel algae growth, when the nutrients can be removed before it has a chance to fuel the algae. there is nothing wrong with using sand in a system either as long as its phosphate binding properties are understood and taken into account.
here is an article with natural reef values and values wanting to be approached in our systems. the only reason why the values do not match is because our testing equipment is not up to par. it has nothing to do with the fact that we do not want them to match. it is this discrepancy that causes all of the confusion in our hobby. we see that phosphate levels are 0.005ppm on the reef and nitrates are below 0.1ppm. yet in the other column values less than 0.03ppm phosphates and 0.02ppm nitrate are acceptable. how? just because we are not able to test for these values does not mean that they should not be our goal. according to
this article the limiting factor for algae growth is 0.009ppm phosphates (converted from micromolar). just because our wimpy test kits read less than 0.01ppm does not mean that they are less than 0.009ppm, let alone the 0.005ppm found on natural reefs. we see it all of the time on forums that they have algae and yet their test kit reads 0 phosphates. 0.0 is far from 0.009ppm. even 0.01 is significantly higher than 0.009. it makes all kinds of sense that people are seeing algae when their test kits read 0, but it does not mean that the phosphates are near the limiting factor for algae growth, does it?
that is why i say. "Friends don't let friends use refugiums".
G~
The proverbial money where your mouth is.
much better place now, i just need to get a decision on where i can put the tank. 
