I have over 200 hermit crabs. Sand and rocks are nice and clean looking.

To Marko and anyone else who'd like to do an experiment :biggrin: :

Could you please take a cup or so of sand from your sandbed (or sump), preferably near or under your rock, put it in a jar with some tankwater and shake it? Post photos of what the jar and your sandbed looks like during this process. I'm guessing the jar water will turn a shade of brown, but that's only a guess.

Looking forward to seeing a whole whack of photos!

I only have an inch of sand bed. But why does it even matter? There's so many successful reef tanks with sand.

My only concern is that it looks clean

You are correct it only looks clean.
I always end up replacing or getting rid of the sand because it gets full of detritus. No meter how much i like the sand if i don't get rid of it in a year or so it always get foul. I never put more then an inch also, And i have about 100x+ water flow in my display tank without counting a return pump flow.

I've been following this discussion, as I am in the process of redoing my upstairs display tank, and need to decide whether to go BB or a thin layer of sand.

Currently, I have about 3 inches coarse sand, and no question it collects a lot of detritus. I vacuum the sand bed regularly, but much of it is inaccessible under the rock. I have high nitrates and phosphates (although lowered recently with bio pellets), and I think this is the main reason.

However, I do like the look of the sand, so at the moment am leaning towards having a thin layer, just enough to cover the bottom, and see how that works.

Another consideration, might be that the sand contributes to the nitrogen cycle, just like the live rock, and eliminating that may reduce the capacity of my tank to manage the bio load with fish and feeding.

When I upgraded from the 10g to the 25g before Christmas 2011, it was on my mind to put a thin layer (under 1") of sandbed at a later date. However, with all the detritus I'm pulling out weekly (with no fish to feed and no coral feeding), I've decided to keep the 25g BB. With the BB, I can see that a lot of detritus accumulates under the rock. Turkey basting gets that crud out from under there where it can be either siphoned out or blasted into the water column for the foams in my HOB to catch and to later be cleaned.

Yes, I looked at your video. But wouldn't a sand bed, with its beneficial bacteria, consume some of that detritus through the nitrogen cycle and go out as skimmate (after the the bio pellets do their job)?

I can see why a deeper sand bed can accumulate N03 and P04, but a thinner one, with good water flow, should help to consume detritus instead. Or is that just wishful thinking on my part?

I don't know what you mean by consume. The sandbed will have nitrifying bacteria, but you will still be left with nitrate and phosphate as a result. At least, this is the way I understand the process.

If you remove the detritus, you remove the resulting nitrate and phosphate - unless you have chemicals that do that for you. I'm not up on biopellets or those things, but I do have elbow grease and don't mind getting my hands wet :)

Video I shot this morning Detritus the Day After Mid-Week Detritus Export. As you will see, there is still detritus in the tank. It only really clears up after I siphon it out during a 20% water change - only to begin reappearing again that night.

By consume, I mean "eaten" by the nitrogen cycle. In other words, you would have less visible detritus as in your video. Instead it would be trapped and consumed by the bacteria in the sand. I can see there would be a limit as to how much the sand can consume, and detritus will become visible if there is too much.

Before I was using bio pellets, my tank was a real mess with detritus and algae covering my live rock and sand. My nitrates went as high as 100 ppm (now less than 20). I had to frequently scrub my rock with a tooth brush, just to try and release more detritus into the water where the flow could move it to my sump with the filter sock and skimmer.

But after I dosed with MB7 and bio pellets, the visible detritus all but disappeared, and I stopped scrubbing my live rock. I still vacuumed the sand bed. But gradually my rocks became clean and shiny with coralline, and the nuisance algae all disappeared. So that's why I think that beneficial bacteria (which need a surface) have a lot to do with a clean tank.

I can only guess that the MB7 and bio pellets are doing what they are supposed to do. Is the water in your pail dirty after vacuuming your sand? How dirty your water is indicates how much detritus your sandbed still accumulates.

I'm wondering if anyone has taken the time to do the sand and tankwater in a jar experiment I suggested earlier in this thread :)