The info below originated from a thread on thereeftank.com about deep sand beds…most of the info was originally supplied by a user who goes by the name Elegance Coral. Some of it has been paraphrased here and there to fit into this article. “EC”, as he is known to many, is well respected for his research of captive marine animals. Not only has he spent years working on the long term sustainability of Elegance corals (hence his user ID), but also researches captive breading methods of various coral species and marine fishes. I’m not sure EC is really a proponent of deep sand beds, but at least we seem to share the same ideas on their myths and what it takes to successfully maintain one. Thanks EC for doing the bulk of the typing here so all I have to do is cut and paste and add a picture or two!
As with every thing else in this hobby, there are benefits and draw backs to using sand as the substrate in a reef tank. Much like the great lighting debates there are die hard DSB (deep sand bed) people and die hard BB (bare bottom) people, so depending on who you talk to you’ll get a lot of conflicting information. When DSB systems became popular many people jumped on the bandwagon of the latest craze and followed the rule of the day. This rule was that you are not allowed to disturb the sand. However, after several years of accumulating detritus in the sand, problems begin to arise. Corals stop growing (or even die), nuisance algae begins to take over, and the overall health of the system plummets. A BB person tells them that it’s the sands fault, so it should all be removed. In the process of removing the sand the whole system gets a good cleaning. The surviving corals bounce back, coralline algae begins to cover surfaces that were once dominated by hair algae, and a new BB person is born. This scenario plays over and over again in this hobby. Was it truly the sands fault though??? No, of course not, but the sand gets the blame. Several years of accumulated detritus was the real problem. The detritus was removed along with the sand which is why these systems improve.
The real problem here is that popular thinking about DSB husbandry is greatly flawed. It is believed that the hobbyist should not disturb a DSB, but rather you should have tons of critters that are constantly disturbing the sand for you. Many false explanations have been offered up for why we should not disturb a sand bed. One of them is that we can release harmful or even toxic substances from the sand. Well, guess what, there is no invisible barrier between substances in the sand and the rest of the system. If harmful substances are building up in the sand, it will only be a short matter of time before they begin effecting the rest of the system. The only cure for this problem is to keep the sand clean so that problem causing substances don’t have a chance to accumulate. In other words, break out the gravel vac and disturb that sand bed.
Another part of the DSB myth that people buy into is that critters can keep a sand bed clean. This is impossible! It takes a lot of detritus to support a relatively small population of detritivores. Sure there are some animals that can help stir and clean a sand bed, but they also leave a lot behind and in the end they are only breaking things down into smaller pieces. A small amount of this may be removed by filtration and/or skimming, but in the grand scheme of things most of this waste is still not going to leave system.
Then there is the whole oxygen gradient setup that will get disturbed if you mess with a sand bed. It is true, the lower areas of a DSB are home to denitrifying anaerobic bacteria, but should we really be concerned about disturbing this? Not in my opinion. Bacteria are very resilient organisms. If they weren’t companies like Clorox and Lysol would be out of business in very short order. We are not going to kill off all the bacteria in a sand bed simply by vacuuming it with a gravel vac. Sure, some of the bacteria will be displaced, but with the vast population of bacteria in a mature sand bed, they will recover very quickly.
I heard another theory that you will need stronger lights in a system that contains a DSB. I believe this is false as well. You do need stronger lights in a dirty system. The presence of a sand bed does not necessarily equate to a dirty system. Dirty sand beds can raise the level of particulate and dissolved substances in the water that block out light, causing the need for stronger lighting. In a clean DSB tank the corals are elevated closer to the lights, reducing the amount of light needed. The bottom of BB tanks generally get covered in dark colored coralline algae and other organisms that don’t reflect much light. Clean white sand reflects a great deal of light. This further reduces the amount of lighting needed. So in my opinion, a properly maintained DSB system would need less lighting than a BB tank.
The benefits to having a DSB include the fact that they do supply an environment for denitification, less lighting may be needed, many of the critters we keep do much better when sand is available and many people find them visually superior to BB. This last one is a biggie for me. All the places I’ve been or seen that have coral reefs all have beautiful soft white sand bottoms. For most of us, myself included, keeping a reef tank is an attempt to mimic the mesmerizing beauty of what God has created in the natural reefs of the world. To me not having sand would be like not having rock or water. It’s just a part of what makes a reef tank look natural.
Now, with all that said, there are some major draw backs to DSB systems. They are much harder to keep clean. In fact, it’s almost impossible to keep the sand clean when rocks are stacked on top of it. Dirty sand beds are a ticking time bomb. In time they will distroy the health of the system, especially if stony corals are a major part of the system. Even well maintained DSB’s will eventually need to be replaced. Bare bottom systems, when set up properly, are much easier to maintain. In a super high flow stoney coral dominant tank they practically clean themselves.
I personally have sand dwelling anemones and other animals that I would not dream of keeping without a DSB. In the end, it all boils down to personal preference, but regardless of what type of system you run, it must be kept clean.
Happy Reefing!