Sand before Rock or vise versa?

[2poor2reef]

Why compact the sand underneath with the weight of the rock? On a natural reef the rock doesn't sit on top of the sand. I would rather maximize the water flow through my entire sand bed.

It seems to me that in an uncompacted sand bed there is a natural stratification of aerobic and non-aerobic layers and that water movement is required to move dissolved organics down into these layers. If you compact an area of sand underneath your rock aren't you restricting water flow to that area and thereby decreasing the aerobic portion of your sand bed? Maybe it doesn't matter much but in my small systems I think it would. Perhaps this is why Shimek's opinion of the minimum useful size of a dsb is so much larger than my personal experience indicates is the case. I run seemingly effective deep sand beds in tanks as small as 10g but I never let the rock sit on top of my bed in those small systems.

 

[npaden]

I did it this way:

1. Isolated base rock in strategic locations to help support planned rock structures.
2. Added approximately 5" of southdown sand.
3. Added RO water.
4. Started the pumps running and added salt to the sump.
5. Waited a week for the sand to clear up a bit.
6. Added live rock.

I don't think it matters tremendously one way or the other. It seemed to work well for me though.

FWIW, Nathan

 

[npaden]

2poor2reef,

I personally have never seen rock suspended above the ocean floor on pvc and eggcrate before. In some instances the reef rock is anchored to a solid foundation of additional rock but in some instances it is actually sitting on the sand or more appropriately buried under the sand as it has been for thousands of years.

I think Shimek feels that the habitat where the sand and rock meet is important for certain microfauna but I'm not sure.

FWIW, Nathan

 

[2poor2reef]

The only reason science has not found that all reefs are sitting on pvc and eggcrate supports is because they haven't dug down far enough.

Obviously, there isn't much natural aboiut our little closed systems. But we are trying to get an end-result that is more natural. In the same way we use artificial pumps and powerheads which are not natural water movement devices (none in the ocean), but what we're trying to achiecve is natural water movement.

There may be isolated instances of coral structures resting on sand but I think it is far more typical that rock is anchored to base rock and that sand accumulates around the reef structure due to coral muching, wave action, colcanic eruptions and all the other natural sand creation methods.

It wouldn't much matter anyway as I understand that relatively little denitrification takes place with the sand bed of a natural reef. Dissolved organics are in such short supply that the vast majority is utilized beforehand. That is clearly not the case in our little closed system. So many opf us are relying on our sand beds to provide a proportionally larger filtration function.

Whether rock sits on the sand or not is a minor point. Since I reef mostly with smaller tanks in the 10-15g range and I make use of deep sand beds it is of interest to me.