The endless sandbed debate...
Hi Bob, 
I was wanting to get your opinion on a few things that no one seems to agree on :)
Ok, I have written you many times before, but I'll give you a rundown of my system. 9 mo old 55 gallon reef, no sump, 70 lbs live rock, good sized skimmer, no other filtration. I have a couple Euphyllia, mushrooms, polyps, Dendronephthya (yeah, I am bad :P). 
<If it lives, not so bad...>
I have probably way too many fish, although my water quality is always good. (yellow tang, 2 neon gobies, pink spot goby, red lipped blenny, dragonet, three stripe damsel, 2 green Chromis, tomato clown, 2 Firefish, purple tang. cukes, cleaner shrimp, pistol shrimp, flame scallop (that's been doing good for about 5 months now). My sand bed is about 2 inches thick "Carib sea special grade aragonite" with a little bit of courser stuff thrown in. 
Now, my problem... My tank has gone through a few radical things, the worst being my removal of my undergravel filter about 2 1/2 months ago. before that I was noticing a lot of copepods on the glass and in the sand, but now I don't really see any (although my dragonet seems well fed).
<Bingo>
I have never seen any worms in my sand, but have seen a few bristleworms on my live rock. Everyone is talking about the value of sandbeds that not only have the bacterial fauna to deal with ammonia, but the macrofauna (??)like worms, mini stars, Mysis shrimp, etc (like Inland Aquatic's detritivore kits) that clean up all the detritus and keep the sand very clean with out any vacuuming or stirring on my part. What I cant get anyone to agree on is whether my live rock will provide these bigger creatures or not. 
<Indeed they will/do>
Some people say no, these life forms don't live on rock, therefore wont come on the rock, others say that live rock makes live sand (or do they just mean a bed of bacteria?). What is your thought on that? 
<A different mix, but tremendous overlap of all organisms, macro and micro on/in live rock and sand/substrates...>
Also, do you think that type of sandbed would be a good thing in my system? I don't want to spend a lot of money ordering a detritivore kit that I may already have naturally in my tank, so any thoughts you have would be appreciated.
TIA,
<I vastly prefer remoted... sump/refugium type sumps for these adjuncts to improved water quality, than trying to do all in the main/display tank... take a long read through the materials stored, and added on to (like this posting) on our site: Home Page 
Rachel >>
<Bob Fenner>

Plenum, sumps setup
I have a 55 gallon standard tank with about 80 lbs Bali live rock.  This is a glass tank, therefore I  installed an overflow about 6 months ago.  This overflows to a small refugium (10 ga) located underneath in the stand.
<This IS a relative to your main tank, small sump... any chance to double plus size it... or more?>
  This tank is composed of three compartments.  The first being an area containing my protein skimmer, heater, activated carbon.  The water then spills over into the next compartment, containing a 4 in live sand bed, with Bali live rock pieces and am growing Caulerpa to assist in nitrate reduction, and also to feed a mandarin in the future.  Next the water spills into the next are containing bioballs, and is then pumped back up into the display tank.  My refugium is lit 24 hrs a day to prevent it from going sexual.
<All sounds good... except my concern should the power or pump go out... do test this... will the water overflow onto your floor?>
My nitrates remain about 10-12.  Located next to the display tank, I have a 15 ga high tank which has been up and running for about 6 months.  My goal is to install a plenum to further help with my nitrate battle.
<A good idea>
I do 10% water changes to each tack every week or so, and each is lightly stocked. (pair of perculas with carpet anemone, 3 small Chromis plus a handful of small shrimp and crabs in the 55, a pink skunk with LTA, and Harlequin shrimp with his chocolate chip star in the 15)  Also I have numerous hermit crabs and snails in all 3 tanks.  My question is; what would be the best way to incorporate this 15 ga with plenum into my other system?
<Actually, ideally, to mount it at about the same level as your current refugium... to ward against the overflow issue... have water run through it 3-4 volumes per hour... overflow into the ten...>
  The 15 ga is a glass tank as well and the water level is just about one inch taller than the 55.  Ideally I would like the 15ga to overflow into the 55 ga, then down to the refugium, and ultimately back up to the 15 ga.  How much would I have to raise my tank in order to do this using a conventional overflow?
<Oh... a few inches... depending on desired flow rate should do it. Know that the "transit volume" in the fifteen will now be additional to that of the 55 should power or pump fail... DO run all with the lowest/ten gallon not filled, turn off the pump/s, see where the water rises to below... drain till it's not overflowing, mark the sump/refugium level with a permanent marker, tape... and NOT fill the sump any higher>
  I'm worried the water being able to drain down the hose and then back up it into the 55 ga without substantially raising it.  Any suggestions would be greatly appreciated and a big thank you to your staff which has gotten my tank to where it is today.
Corey
<Really wish you could add more volume underneath... do look into a container you can tie into the current refugium to take up the excess volume if you can't switch out the ten for something larger. Bob Fenner>

A Plenum Pro In The Making!
Hello! Thanks for all of the great info!
<Our pleasure! We're happy to be here for you! Scott F. here today...>
I was reading about DSB’s and everywhere I am seeing stressed over 3 inches to avoid nutrient sinks and the support of efficient denitrification.
<That is the prevailing thought...1/2" or less, or 3" or more...>
I am using a plenum constructed with lighting grid supported on ½ PVC caps with an overall height of approximately 1 inch. Now, my sand bed is on average 4 inches including the sand depth. The sand is a medium grain size. My local pet shop said that the grain size was specifically set up for plenums as the grains allow more water flow to the plenum. Am I creating a nutrient sink?
<First- with regards to sand grain size to use in plenums, you are well advised to use 2-4mm size, as this sized grain will help establish dissolved oxygen gradients throughout the bed. Sounds like your dealer is right on. The depth of the sand/plenum is really an absolute...the dimensions have been arrived at through much research by experts in the field, such as Goemans, Jaubert, etc. One to one and a half inches high. You're right on again! Four inches is the recommended sandbed height, too. Everything that you've done is consistent with the established "specs" on plenum system construction. With sound maintenance, overall good husbandry, and excellent observation on your part, you'll be in great shape. I see nothing wrong with your plenum>
My Nitrates are 6ppm between weekly water changes, 0 nitrites, 0 ammonia, and Phosphates I am unsure of because I think my test kit is bad. 
<Do get a new phosphate test kit...A worthwhile expenditure, IMO!>
Should I add another 1” of sand? ‘Cause if so my wife is going to strangle me!
<Just stick to your plan. No need for an additional inch, IMO. A deeper sandbed over the plenum could actually be a negative, resulting in lower sandbed ReDox levels due to higher levels of nitrogen being stored in the sandbed. You've followed the principles of plenum construction to the letter thus far. stay with it. Good luck! Regards, Scott F.>

- Plenum Questions -
Hello! Thanks for all of the great info!
I was reading about DSB’s and everywhere I am seeing stressed over 3 inches to avoid nutrient sinks and the support of efficient denitrification. I am using a plenum constructed with lighting grid supported on ½ PVC caps with an overall height of approximately 1 inch. Now, my sand bed is on average 4 inches including the sand depth. The sand is a medium grain size. My local pet shop said that the grain size was specifically set up for plenums as the grains allow more water flow to the plenum. Am I creating a nutrient sink? 
<You're probably on the edge of such things, but I would give it some time. We get a lot of questions from folks who have just set up such systems wondering why they have any nitrates at all, and the truth is it takes months for the plenum and deep sand bed to become fully active and working. They are not instant fixes.> 
My Nitrates are 6ppm between weekly water changes, 0 nitrites, 0 ammonia, and Phosphates I am unsure of because I think my test kit is bad. Should I add another 1” of sand? 
<I would, really the more the better here.> 
‘Cause if so my wife is going to strangle me!
Best wishes, Scott R.
<Cheers, J -- >