Setting a reef tank takes a lot of thought and planning. Aquarists sometimes overlook the importance of the substrate. At first glance, the substrate is just a decoration. It’s there to cover the bottom of the aquarium. But it’s much more than just some sand. You may remember bare-bottom reef tanks. The idea was to prevent accumulation of debris by removing substrate particles that trapped organic sludge. The bare bottom was supposed to allow debris to be blown up and into the filter system, keeping the tank pristine. Jumping ahead to today, we now know it’s possible and beneficial to have a layer of sand substrate in a reef aquarium. But there’s more to it than simply dumping substrate on the bottom of the tank. There’s some real science involved if you want your sand bed to work properly. Curious? Here’s what you need to know about sand beds.
The main engine that drives our reef aquariums are billions of invisible microbes laboring away to recycle nutrients and remove toxins. This unseen word works day and night, mostly invisible to our eyes. A lot of these microscopic life forms live in and on the rock. They’ll also set up shop in the substrate. In general terms, sand beds provide a place for beneficial microbes to colonize. But the type of sand and depth of the sand bed has an affect on what kind of microbial action takes place in the aquarium. Sand beds fall into two categories. Shallow beds are normally 1.5 to 2 inches deep. Deep sand beds can be up to several inches thick. The size of sand used in each category also affects sand bed performance. We’ll break it down.
A 1.5 to 2-inch fine sand bed looks silky smooth. Popular substrates are Fiji Pink and Aragamax sand. You’ll have plenty of extra surface area for aerobic bacteria. The sand is light and can be blown around if you’ve got strong flow pumps. It may result in exposed bare spots on the bottom of the tank.
A 6 to 8-inch bed of fine sand will have that smooth look plus the benefits of aerobic and anaerobic zones. That’s because the deeper layers won’t be constantly blown around and exposed to oxygenated water. You’ll want to have a sand-sifting clean-up crew to pick through the sand grains. They’ll keep the deeper layer free of sludgy detritus but won’t upset the low-oxygen zone. The down side is the deeper bed requires more sand, which reduces space and water volume in the aquarium.
Another popular option is to create a shallow bed using coarse grained sand. There’s less surface area, but it won’t make any difference in the big picture. The heavier, more dense particles won’t be blown around by wave pumps. The coarser particles will act as a detritus trap. Some organic matter is great, acting as a food source for the microbes. But too much can lead to hydrogen sulfide pockets. A clean-up crew will help along with modest feeding with frozen and prepared foods. You can easily clean it with a gravel vac while making a water change.
We say “Don’t do it!” Deep coarse sand beds are tricky. They will eventually clog with organic sludge and become pockets of anaerobic activity that produce poisonous hydrogen sulfide. It’s better not to risk it and in reality, you can achieve better results by using a deep bed of fine sand. You’ll get the denitrification, great looks but without the difficult to maintain sludge layer. How much you need depends on type of sand and footprint of your aquarium We’ve made it easy to figure out with our marine Depot Sand Bed Depth Calculator! Just put in your tank’s dimensions and type of bed you want to build. You’ll also have to plug in the density of the sand product you want to use. This can be found on the product description page. It’s easy! No more guessing!