Substrate Options

Substrate Options for the Marine Aquarium

When setting up a new aquarium, one of the first items of consideration after determining the type of tank you want is which substrate to use. There certainly are no shortages of options, or opinions on which is the best substrate to use. We will look at what some of the most common options Crushed Coral, Bare Bottom, Sand (both Shallow and Deep sand beds), as well as Plenums. We will also take a look at some of the pros and cons associated with each substrate choice. Please note there is no right or wrong substrate, it is a matter of personal preference. Each person has their own opinions and understands the levels of maintenance they are willing to dedicate to their aquarium.

Crushed Coral

Cost: Approx. $1 - $1.50 per lb.

Crushed Coral is one of the most frequently used substrates for new saltwater hobbyists. This is mainly because of its bright white color and lower cost when compared to bags of live sand displayed next to it in the fish store. Crushed Coral is a great choice due to its propensity to keep both pH and calcium at optimum levels for a healthy reef tank.
The negatives of crushed coral include the lack of marine animals adept at living within the substrate. This means that the detritus and waste that collects under the CC must be manually removed fairly regularly. Without regularly vacuuming of the gravel, waste will build up and cause nitrates to raise to unhealthy levels. Without the vacuuming the CC with appear dirty and will not retain the bright white coloration that made is so appealing in the store.

Although Crushed Coral does require maintenance it is not a phenomenal amount necessary to successfully use it as a substrate. By using a gravel vacuum when performing water changes most of the detritus can be removed and the gravel turned to retain the preferred coloration. The difficult part of this is trying to get behind rockwork or in to corners. Without being able to clean the whole surface area, excessive fish waste can breakdown and cause ammonia and nitrate to increases to unsafe levels.

Bare Bottom (BB)

Cost: Free

One option that is becoming more popular is not using a substrate at all and setting up your reef directly on top of the glass bottom of the aquarium.
By not using a substrate you can achieve a mirror like effect on the bottom of the tank (until coralline forms anyway). With just a glass bottom there is nowhere for detritus and waste to accumulate and cause parameter issues. The bottom does not require cleaning, or animals to turn and sift the sand. Unfortunately there is also noting to act as a buffer to assist in keeping PH values at optimum levels for fish and coral health.
One of the biggest drawbacks I have found is the instability of any rockwork created within the aquarium. With sand or crushed coral the base rocks can be situated in to, and held in place by, the substrate. With a bare bottom tank there is nothing to hold the base rocks in place allowing them to potentially wobble in the current. Rocks tumbling for the top of the rockwork can have disastrous results. One method of combating this is to drill the LR and insert rods of either Plexiglas, acrylic, or PVC to stabilize the formation. Others have used epoxy to attach rocks to one another, however this will make it incredibly difficult to remove rocks from the tank or re-aquascape. A newer method of protecting the tank bottom and stabilizing the rockwork is to use starboard cutting board.
The mirror look of the tank bottom will disappear as coralline algae will grow on the glass bottom of the tank, which may be a bonus, or a headache depending on your personal views of the appearance of coralline algae.

The main advantage of a BB tank is ease of maintenance. With the ability to power sweep the bottom of the tank there is no area for wastes to accumulate. Rockwork can be stabilized via methods mentioned above, but that does require a significant amount of work and severely hampers your ability to re-aquascape the aquarium later without a complete teardown. If you choose the “balance” method of stacking rockwork you run the risk of a rockslide and damaging the tank or livestock.

Shallow Sand Bed (SSB)

Cost: $3-$30 depending on type of sane and size of tank
Depth: Generally considered less then 3 inches

A shallow sand bed can be aesthetically pleasing and relatively inexpensive to create. While you could certainly use the Live Sand sold at your local fish store (approx. $1.60 per lb) you could just as easily use the white play sand sold at your local Home Depot or Lowes store (approx. $.08 per lb.). If unsure if the brand can be used safely in the aquarium post as much information about the sand on your local forum.Avoid the tan play sands as they contain metals and other trace elements that are not healthy for an aquarium. A 50 lb bag generally runs a little more then $3. The Colorscape sand available a Kmart works and retails for $3.99. Over time the bacteria and micro-fauna will grow and reproduce in your store bought play sand bed making it “live”. Your local reefers are a good source for live sand to seed your new sand bed.

Sand is popular because it is natural, inexpensive, and aesthetically pleasing due to its coloration. It can be easily maintained by aquarium “critters” such as snails, conch, and hermit crabs. A shallow sand bed will provide adequate stabilization of rockwork, as well as area for copepods and other smaller organisms to live, providing a food source to some aquarium animals.

A SSB does not require significant maintenance and merely needs to be turned occasionally to retain its coloration, and to prevent the build up waste and nitrates. Often times the turning can be, and is, performed by the animals in the aquarium themselves, preventing the need for additional maintenance by you.

A SSB will not provide enough anaerobic space to breed anaerobic bacteria to combat nitrates as a Deep Sand Bed will. Sand also has the potential to be blown around if the flow in the tank, or specifically in one part of the tank is too high creating BB spots and sand dunes in others.


Deep Sand Bed (DSB)

Cost: $3-$30 depending on size of tank
Depth: Generally considered 4 inches or more

Deep Sand Beds (DSB) are gaining in popularity as more research is being done on the effects on anaerobic bacteria in the aquarium. These are generally the same principal as a SSB just deeper.

A DSB provides an environment for anaerobic bacteria to populate and reproduce. The benefits to anaerobic bacteria are pretty isolated around their ability to attract and remove nitrates from the water column. Thus preventing nitrate levels from getting too high and causing stress and damage to your livestock. Because of the deep levels of sand and the lower O2 levels the ph is lower which aides in dissolving aragonite sand to act as a pH buffer.

The concern about the DSB is the chance that it will “go bad”, meaning since it stores nitrates in the lower levels of the sand bed, if these levels are disturbed the stored nitrates are released in to the water column simultaneously causing a very high, very fast nitrate spikes. A DSB will also create and maintain Hydrogen Sulfide, which if released due to disturbance of the sand bed will cause major issues and die-off in the aquarium. One other complaint is that a DSB takes up valuable real estate in the tank. The trim around the bottom of a tank is only about an inch tall. Depending on personal preference, looking at the sand stacked up 3 inches higher then the trim may not be very aesthetically pleasing. A great source for additional information rregarding DSB can be found here: DeepSandBeds

Plenum

Cost: Less then $20 in material.

A plenum is a space under a sand bed that only contains water. No light can get to it, and is used strictly to harbor anaerobic bacteria. If you’ve never seen a plenum imagine screen door the size of the bottom of your tank elevated by PVC feet. Sand is then placed on top of the plenum to make a DSB. A plenum provides a great means to create anaerobic space to assist in the removal of nitrates from the water column.

Plenums have not become very popular in the hobby. Like deep sand beds, they run the risks of “going bad”. They take up a significant amount of space within the aquarium, and do to the fact that they need to be kept dark require either painting or covering the bottom of the aquarium with a opaque material to keep light from the refugium (assuming yours is under the stand) from defeating the purpose of the plenum by lighting from underneath.
Plenums are a great means of reducing nitrates as the anaerobic bacteria are significantly better at removing nitrates then their aerobic counter-parts. Given the amount of real estate plenums take up, they are really only visually attractive in a taller then average tank.

Summary
This article only scratches the surface of options you have available, and does not go in to the different variations of each option mentioned above. These are the most common and basic of substrates, and this should give you a fairly decent understanding of the differences of each as well as some of the pros and cons of each. I encourage you to think through your set-up process, and research everything, including what type of animals you'd like to keep, amount of time you're will to spend on maintenance, what you consider asthetically pleasing, and fuction over form, before selecting a substrate.

great write up!!!

I like my DSB. I do have higher nitrates right now but I think that's all self inflicted.

Nice summery Craig. I like the way you listed good and bad for each without saying your way is the best/only way.

Great job craig! ....one of the issues we had with crushed coral is when you can't get to the stuff under rocks and corals, after a while it "grows" together and becomes a slab of cement ... we currently have a bare bottom in our main display tank and I'd have to agree with YOUR pros and cons....it's a tough call as to which will work best

Originally Posted by Pat B

Nice summery Craig. I like the way you listed good and bad for each without saying your way is the best/only way.

Great write up, But Plenums were used in the early days of reefing here in the states. I used them extensively in Salt tanks in my days, The key to a plenum putting stand pipe leading to the bottom area, put a power head and let run. After your nitrates stabalize, you can cap the stand pipe. Garf still uses them on thier "Bullet proof" reefs and I must say that Sally Jo's reef are beautiful.

here is some examples:





All these tanks use plenums method and the top one has been up 7 years.

Nice thread Craig.

I'll stick with my shallow sand bed.

Yep same Bill But back in the early days it was really a nice option for those that didnt know the Berlin method.

That is all awesome info.
I have had crushed coral (in my 1st tank), sand in this one, and have since syphoned out the sand for a bare bottom.

CC and sand IMO, are the same as far as maintenance and such, excluding of course DSB's. I have no idea about those...

But one thinG I wanna ask...
Why do I keep reading that CC acts as a buffer and helps keep calcium levels up?
I even see that on the bags it comes from! Is this because it's what we put in our reactors? I just don't buy it! When I had cc I still had to dose a 1/4 cup of a and b daily!
Cc cannot act as a ca and alk supplement without the co2... Unless there is something I'm missing!

I am trying to find more info, but everything I come across references fresh water. Where the ph is 6.6 to 7.2. Not "that" makes sense to me, but I'll keep reading...

I don't think it keeps calcium level up (at least not to where we would want them). I think it acts more as a PH buffer. As PH drops the coral starts to breakdown - thus increasing PH.

When I ran CC in my 1st tank I never had to buffer for PH. Now that I run sand I do.

Awe geez, this self correcting iPhone...

After 7.2 in my above post, the word "not" was SUPPOSED to say "now"

Originally Posted by Tizzo

But one thinG I wanna ask...
Why do I keep reading that CC acts as a buffer and helps keep calcium levels up?
I even see that on the bags it comes from! Is this because it's what we put in our reactors? I just don't buy it! When I had cc I still had to dose a 1/4 cup of a and b daily!
Cc cannot act as a ca and alk supplement without the co2... Unless there is something I'm missing!

I dont buy it either. In order for it to act as a buffer it needs to dissolve like in a reactor. IMO the PH in sand beds cant get low enough to dissolve like this. We had a 6" DSB for like 5 or 6 years and it was just as deep when i yanked it a few months ago. I think its more of a sails pitch then anything else.