Why are there bubbles in the substrate?

For the past couple of weeks we have been noticing bubbles in the substrate of our tank. To find out if this was normal and acceptable, we did some research online. As with all topics related to saltwater aquariums, we found a variety of answers and opinions, but the consensus was mostly yes, it is normal and good to have bubbles in your substrate. But what are they?

Why are there bubbles in the substrate?

The substrate in our tank can be classified as a DSB, or deep sand bed. Although fairly shallow in term of other aquarists DSB, it is roughly 3 inches deep in most places. Having a deep sand bed allows anaerobic bacteria to grow and convert the nitrates to harmless nitrogen. Nitrate levels are usually maintained by regular water changes in the aquarium. The conversion of nitrates to nitrogen by anaerobic bacteria is also a helpful method.

This is part of the nitrogen cycle that isn’t usually discussed. These bubbles of nitrogen get trapped in the sand and get released when the bubbles get large enough to break through the surface or when the substrate is disturbed. Our Cerith snails are great for this. They stir up the top most part of the substrate in search of algae and other detritus and release the nitrogen bubbles. I was concerned at first, thinking they may decrease the anaerobic bacteria population by aerating the substrate too much, but bubbles keep forming in our substrate and we haven’t had any problems so far. Our nitrate levels are consistently low or zero, and our fish and corals seem to be thriving.

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