Coral rocks in the sand

[raeh1]

Coral rock..

I know people have sandless tanks and others with the rocks sitting above the sand.

In the sea the rocks sit in the sand. So why is it better in a marine tank to do this..

I am just considering my options at the moment.. currently my rocks sit in the sand with limited to nil flow behind them and I haven't had many problems.

suggestions please.

[Feelers]

I thought it was to prevent detrius buildup. I think the idea is that when the rock sheds you want to be able to remove it instead of having it gunk up in the sand. Not too sure though.

[HelifaxNZ]

All the books I've read say to lay the rocks down first, then the sand as this will give the rock formation stability and any sand sifters could dig underneath the rocks and make the whole structure colapse.

[chimera]

I thought it was to prevent detrius buildup. I think the idea is that when the rock sheds you want to be able to remove it instead of having it gunk up in the sand. Not too sure though

pretty close. nitrifying bacteria (converts waste to nitrates) exist in the rock and sand and require oxygen (aerobic) to survive. putting rock directly on sand essentially means smothering them, hence one reason for using a reef rack.

[lduncan]

In the sea the rocks sit in the sand. So why is it better in a marine tank to do this..

Rocks absorb whatever they are sitting in similar to a paper towel in water.

If you have rocks sitting in a sand bed, they absorb the nutrients which are stored in the bed, this can fuel problem algae. You could end up wondering why you can't detect phosphate in the water yet the rock is covered in nasty algae.

If you have a water gap between the rock and the sand, then there is no absorption taking place (until the sand bed fills up and starts leaking)

Layton

[chimera]

yeah, and what layton said to further clarify my comment above, you already have enough denitrifying bacteria (anaerobic or anoxic, dont require oxygen) inside your rock. these bacteria convert nitrates (created by nitrifying bacteria) into nitrogen gas. so, the idea is to maximise the amount of nitrifying bacteria on the surface area of your LR (again, they are aerobic so require oxygen to survive) to break down the initial waste. comprende?