If you're setting up a refugium for some denitrifying benefits, I would suggest using fine sand, 4 inches depth. Be sure that no crabs or shrimp are in your refugium, because they will eat any beneficial life that takes up residence there.
The refugium will not be sufficient to take care of all the filtering requirements that your display tank requires, but it will be very interesting to watch what develops in there after a few months.
:smile:

i have a 40 gallon breeder which i will plumb to a 25 gallon sump. i have a reef octopus extreme 160 skimmer which i will use. i plan on using this tank as a grow out for juvi clowns so there will be a huge bio-load. i want to keep the tank bare bottom so i can siphon out detritus as it builds up. you said the refugium will not be sufficient enough to take care of all the filtering requirements so what do you suggest i do for filtration? after putting the skimmer in the sump there isnt a lot of room so i was thinking of using a DSB and chaeto......

If you have an in sump skimmer and you wanted sand in there as well, were you going to bury the bottom of it in sand, or is there a separate compartment for the skimmer?

For filtration, you can use live rock, skimming, activated carbon, gfo (granular ferric oxide for phosphate removal) and water changes.

What were you planning on feeding the juvi clowns?

i was going to put in baffles and section it off. do you think a DSB and a lot of chaeto would be ok i dont really want to put any live rock as there isnt much room in the sump

the juvies will be fed a variety of foods from new spectrum pellets, flakes, brine shrimp, mysis, krill, and home made mush! :mrgreen:

The chaeto will help, definitely. The sand will be interesting to watch what develops.
You'll know that the sand bed is getting overwhelmed if detritus settles on it for any length of time (quick, like more than 1/2 hour).
Sand beds take a couple of months to develop before they can really start processing the waste.
If you're not placing any corals in there you could also incorporate some filter socks into your filter system.