Substrate Selection - A primer
1) Looks are not everything.
1.1) When I look at an aquarium. I see Living art. The design of an aquarium is a direct expression of the owners creativity. Even though many of us may not realize it, a well designed aquarium is also an expression of the owners knowledge in subjects such as Animal Behavior, Biology, Microbiology, Physics, Chemistry, & Geology. So for now at least lets explore a little Geology and Chemestry.
1.2) Besides the stand one of the most visible components of your aquarium can be the substrate. Whats the best substrate a person can use in an aquarium? There is no one answer to that question. First of all we should have an idea of which types of fish we will have. .Different species of fish come from different environments and would be happier in a similar environment to that which they naturally inhabit. Some hobbyists choose to set up "themed" tanks these are also known as "
Aquarium Biotopes". Basically an "
Aquarium Biotope" is as if you were to go to a specific environment say a river and take a snapshot of a section of that environment. In such a scenario you would only choose the substrate, fish, decorations and plants that are indigenous to the environment you wish to represent. "
Aquarium Biotopes" are lots of fun but can be very challenging because some species of fish and plants require very specific conditions of water quality and lighting in order to thrive. The average hobbyist just considers the environment the fish they wish to keep comes from and tries to keep that in mind as they choose the substrate. Most lakes and rivers have a sandy bottom. Many species of fish enjoy digging in the substrate. In those situations sand can be a wise choice. Some streams and lakes have areas with a very rocky bottom. And fish from those environments would often prefer gravel as substrate in their tank. Most fish enjoy a "Planted" environment or the owner might specifically wish to keep a highly "Planted" aquarium. When growing aquatic plants, the Captation Exchange Capacity (CEC) is also an important thing to consider when choosing a substrate. CEC is the ability to adsorb positively charged nutrient ions (so high CEC is good). This means the substrate will hold nutrients and make them available for the plant roots. It should be noted however that CEC doesn’t indicate the amount of nutrients the substrate contains. Some manufacturers produce special substrates for use in planted tanks. Some are designed to be mixed with gravel or sand, whilst others can be used alone. They are usually clay-based and rich in iron and other nutrients and trace elements required by plants. A good example of a preferred substrate for planted aquariums is latterite, or a mixture of latterite and sand.
*Special Note* aquarists using UGF (Under Gravel Filtration) can only use gravel type substrates because most other choices will lead to problems in flow and dead spots throughout the substrate. Which ever substrate you may choose the general rule is to use one pound of substrate per gallon of water that the aquarium contains.
1.3) Ok so we have a general idea which fish we wish to keep and we know how much substrate we will need. What other factors should we consider? Substrate basically boils down to four major factors:
1.3.1) Color
1.3.2) Size
1.3.3) Reactivity to water
1.3.4) CEC
2) Lets look at the different types of substrate available then we will examine how the above factors fit into helping you decide.
2.1) No substrate - AKA Bare bottom
2.2) Glass Marbles/ Glass Disks
2.3) Gravel
2.4) Latterite
2.5) Peat
2.6) Sand
2.1.1) Introduction to Bare Bottom Tanks
Many hobbyists enjoy bare bottom tanks. Especially those with very messy fish (Fish that present a very heavy bioload to their environment. Some examples of fish that fit into this category are: Large fish, Predators, & Goldfish. A hobbyist keeping these types of fish might use bare bottom tank so that they can easily identify waste material. Many large fish tend to move things around the tank, A bare bottom tank is one way to avoid having to constantly reorganize the substrate due to the activities of such a fish.
A Bare bottom tank with a choice selection of decorations also has a very "Abstract" "Minimalist" art look to it.which many hobbyists find attractive. Bare Bottom is also a preferred choice in Quarantine/Hospital tanks because in addition to the features listed already it is also easier to sterilize the tank once treatment or quarantine period is completed.
2.2.1) Introduction to Glass Marbles/ Glass Disks
This is also a popular choice in Quarantine/Hospital Tanks for those who cant stand to see a bare bottomed tank because glass has a very small surface area making it very similar in features to having a bare bottom tank.
2.3.1) Introduction to Gravel
Gravel is the most common substrate in use in fresh water aquariums. Aquarium gravel can be as coarse as pea-sized or almost as fine as sand.
Three to four millimeters is widely considered the best size to promote optimum water flow throughout the gravel. Gravel is available in a number of colors, and may be naturally colored or dyed. Gravel sold specifically for use in an fresh water aquarium are chemically inert. Some brands actually have a polymer seal to ensure they do not affect water chemistry
Gravel for aquarium use is commonly composed of quartz or other lime-free minerals.
If the gravel is rough or sharp, it should not be used for bottom-dwelling fish that like to sift the substrate or dig.
For the reasons mentioned above if you get your gravel from an outdoor home and garden supply shop or Hardware Store it is very important to pay close attention to the material the gravel is made of. For instance Marble chips, Holly Rock, Lime Stone, and Coral are all calcareous materials. They react to water, making the water hard and of a higher PH. This would be useful in a tank containing fish that prefer high range PH. Such as Salt Water fish or African Cichlids. But fish that prefer average PH or even softer water will not do well with these materials as a substrate.
2.4.1) Introduction to Latterite
Laterites are clay soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. Most of commercial laterite is mined from the US in areas that were tropical 200million years ago.
2.4.2) Many Aquatic supply manufacturers have thier own versions of laterite. One of the more popular brands is by Seachem its called Flourite and comes in several colors and textures (Black Sand Flourite makes an excellent substitute for sand):
Original Flourite
Red Flourite
Black Flourite
Black "Sand" Flourite
2.5.1) Introduction to Peat
Peat, or decomposed plant matter, is used most commonly in soft water or blackwater river systems, such as those mimicking the Amazon River basin. In addition to being soft in texture and therefore suitable for demersal (bottom-dwelling) species such as
Corydoras catfish, peat is reported to have a number of other beneficial functions in a freshwater aquarium. It softens water by acting as an ion exchanger, it contains substances good for plants and for the reproductive health of fishes, and can even prevent algae growth and kill microorganisms. Peat often stains the water yellow or brown due to the leaching of tannins.
2.6.1) Introduction to sand
When it comes to sand for your aquarium there are many choices. Sand is rapidly growing as a choice for aquarium substrate. Several of the more popular choices are::
2.6.1.1) Silica (Silica – Silicon Dioxide) - Many sands used for sandblasting contain Silica. However you must be careful because not all of them are pure silica or contain silica at all. A popular source for this type of sand is swimming pool supply outlets. Where it is sold as "Swimming Pool Filter Sand"
2.6.1.2) Silica is completely Inert in fresh water aquariums -silica sand is 99.0-99.9% SiO2
and is considered "totally insoluble" in water according to the US MSDS. This means that it will not change the parameters of your aquarium water such as PH. It should also be mentioned that silica is not good in a marine aquarium as it promotes the growth of marine algae.
1.2) Play Sand - (Used for sandboxes) which you can purchase at most building supply/hardware hardware stores. Many sands sold as "Play Sand" contain materials other than Silica.
For instance one brand of "Play Sand" by QUIKRETE® marketed as "QUIKRETE® Premium Play Sand® (No. 1113)" contains Limestone & Crushed Quartz. - If you change the water in your aquarium often then you wont notice anything but if you skip a few then the limestone can make your PH rise.
1.2.1) Play Sand and Sand Blasting sand both fit into the "Unknown" catagory and for this reason it is best to avoid them unless you are positive of exactly what they contain.
1.3) Black Beauty - this also very popular in the sand blasting industry It can be purchased online and also in hardware stores, you can sometime get this from places where sandblasting is done. It is made from powdered iron slag (Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide).
1.3.1) Slag as mentioned is Powdered Iron slag as the name implies it contains iron which means it is not inert in either salt water or Fresh water.
1.4) Coral Sand - is sold online and in LFS.
1.4.1) Coral Coral is made by millions of tiny carnivorous (meat eating) animals called polyps. Polyps live in groups called colonies.
Each polyp builds a case of limestone around itself, using calcium from the water. It is like a house, with a floor and walls. This remains after it has died and forms a foundation for another polyp to build a house on, putting a floor on the roof of the old one. When these limestone formations increase, they are called a coral reef. As time wears on these formations die and fall apart and become natural reef coral sand that is collected the ocean.
1.5) Aragonite - also is sold online and in LFS.
1.5.1) Aragonite is a carbonate mineral, one of the two common, naturally occurring crystal forms of calcium carbonate, CaCO3 (the other form is the mineral calcite.) It is formed by biological and physical processes, including precipitation from marine and freshwater environments.
*NOTE* Both Aragonite and Coral Sand are both calcium based so they both will increase the PH of an aquarium that contains them. Many keepers of African cichlids and Marine fish prefer these types of sand because they need the higher PH to maintain the proper environment for thier fish. If you are not intending to keep the above mentioned it is best to avoid these types of sand.
1.6) Black Tahitian Moon Sand - which is rumored to be made from quartz it is also is sold online and in LFS.
1.6.1) Quarts is inert when placed in either salt water or fresh water aquariums.
2) Appearance and preparation for use
2.1) Silica -is a very light tan or off white in color and is very uniform and fine in grain size. It very easy to clean and provides a sharp look to an aquarium,. It is also extremely affordable..
2.2) Play sand - just as affordable as Silica but it is darker and less uniform in grain size & color than Silica sand. It often contains clay and other non essential materials. This can often make it very dirty compared to Silica sand. Requires considerable cleaning and once again I stress that you make sure you know exactly what it contains.
2.3) Black Beauty Obviously quite black in color it is another affordable sand for use in aquariums. Although as mentioned earlier it isn't really sand. It's really not recommended for fish that root around in the substrate because by design it is very sharp. In my opinion it is one of the least suitable choices of the list. It also should be noted that this stuff requires extensive cleaning.
2.4) Coral Sand this is one of the more expensive choices one can make. It comes in a variety of colors including off white and a nice rosy shade. It is considerably Lighter and less uniform than most other sands. As mentioned earlier it is great for aquariums that require a high PH range. Relatively easy to clean although can be dusty.
2.5) Aragonite is is available in a wide range of colors & sizes. It is expensive, however it costs less than Coral Sand. Otherwise it is the same in cleaning requirements & PH buffering properties
2.6) Black Tahitian Moon Sand, is the best choice if you want black sand. It really looks striking in an aquarium. It varies in cleaning requirements, so be prepared some batches can require extensive cleaning. It costs about the same as aragonite.
"So Now that you know all about sand I will tell you which I prefer and list out the "Pros" and "Cons" of my favorite. Most of the points I contrast also apply to any sand you may choose (Except where specifically noted)."
3 ) Swimming Pool Filter Sand as Aquarium substrate
Swimming Pool Filter Sand
"Mystic white" Angular Pool filter sand by U.S. Silica 1-800-258-2500 it is inert and very pretty. See if you can get the large size I got standard and I like it but I think bigger grains would have been better as an after thought.
4) Pros Of Swimming Pool Filter sand in a fresh water aquarium:
4.1) It is very clean since it is made for swimming pool filtration, I lightly washed the sand the first time I set this up. On the second tank I set up with sand I didn't wash the sand at all just rinsed it once. - They both had the same settle time.
4.2) It doesn't "Compact" as much as other sands
4.3) Swimming Pool Filter sand is quite heavy it doesn't cloud up when moderately agitated. I have Balas and they are moderate substrate diggers, I'm not sure what it would be like with hardcore diggers ie: "Geo's". It wont get cloudy in any case but my concern with hardcore diggers is instead of using the siphon method I listed above you might instead actually dig in the sand using the normal fatter end of the siphon tool to get some of the poop as I imagine fish like "Geo's" will bury some of it in their daily rooting about.
4.4) Swimming Pool Filter Sand is more specifically designed to be more "Angular" than other types of sand.
This is so that it can trap debris more effectively. The benefit in an aquarium is that it has more surface area which in turn provides more colonization surface for beneficial bacteria. It is a point of contention by some people that this angularity is bad for fish with soft mouths. Throughout my research and my 2 years of use with this product I have never actually found any supporting evidence to this claim.
4.5) The color is very attractive
4.6) Completely Inert in fresh water aquariums -silica sand is 99.0 - 99.9% SiO2 (Silica – Silicon Dioxide)
and is considered "totally insoluble" in water according to the US MSDS.
4.7) Can be mixed with other substrate materials to achieve what is considered by some to be the perfect mixture for a planted aquarium.
5) Maintenance in an aquarium with sand substrate.
Having sand in an aquarium is very similar to bare bottom when it comes to maintenance, Many sand owners with quartz based sand report having no trouble vacuuming the substrate just as they normally would with gravel. However some others as well as most "Silica" based sand owners report having trouble vacuming their substrate. A lot of sand owners solve this issue by purchasing a very narrow gravel vac. I have learned over the years there is a simpler method.
Basically you Remove the larger tube from the hose. Use the hose by itself and lightly skim the surface Making sure you don't touch the sand. In time with practice you will find the right height to keep siphon to just get the poop and muck and leave the sand in tact.
(Image#1) Dont Use larger Portion of tube for sand
(Image #2) First Start siphon as you normally would.
(Image #3) Next Disconnect Larger tube from hose
(Image #4) Now hover over debris but do not touch surface of sand.
(Image #5) With a little practice you will find the perfect height to get the degris and leave the sand in tack (Well most of it anyway)
*Note*If you have a planted aquarium especially with delicate leaves be very careful using the above method, The suction on the tube is increased dramatically when you remove the wider portion of the assembly and may snatch plants if not watched closely.
You will find if you grade your substrate the poop and ditrus will collect in specific areas according to the currents in your tank, just like it does when you have a bare bottom tank.
5) "Cons" Of Swimming Pool Filter sand in a fresh water aquarium:
5.1) Many Complain that it is more difficult to manage rooted plants in an aquarium that has sand as a substrate
5.1.1) Completely Inert in fresh water aquariums -silica sand is 99.0-99.9% SiO2 (Silica – Silicon Dioxide) and is considered "totally insoluble" in water according to the US MSDS.Thus when used alone as a substrate it it lacks other minerals such as iron that are important to plant roots!
5.2) Dirt and debris are more visible especially with white sand.
5.2.1) This means it must be cleaned more frequently in order to keep the appearance of a clean tank even though there is the same amount of debris as other types of substrate.
5.3) Does not work with Under Gravel Filtration.
5.4) Extra care must be taken in
Acrylic aquariums to guard against excessive scratching.
5.5) Some complain that sand can create anaerobic pockets of toxic gas in the aquarium if the sand becomes compacted and is not frequently "Stirred"
Examples: Recommended substrate choices
| Type of Aquarium | Recommended substrate material |
| General community tank | Natural pea sized-gravel or pure silica sand |
| Planted tank | Fine lime-free gravel and/or nutrient substrate additive ie: Peat, laterite |
| Soft water fishes | Lime-free gravel, Pure silica sand, or Peat |
| Cichlids from hard water, Marine Aquariums and invertebrates | Marble Chips, Aragonite or coral sand |
| Breeding tanks | No substrate or thin layer of silica sand |
| Quarantine/Hospital tanks | No substrate, Glass Marbles, or Glass Disks |
6) My thoughts on anaerobic pockets.
Type 2 (Ref # 2.1.2) is most common and pretty harmless. In fact there is a form of filtration called "Plenum" in which one deliberately creates an anaerobic region at the bottom of the tank under the sand so that anaerobic bacteria can process nitrates in that space. Users of that type of filtration state that the by product of this process is Nitrogen gas which simply leaves the tank through the surface not effecting fish at all.
There are two types of gas that in theory can be formed anaerobically in an aquarium:
3.1) Types of anaerobic pocket gas
3.1.1) If rotten egg odor = Hydrogen sulfides gas. In high concentrations this can wipe out a tank.
3.1.2) If no odor = Nitrogen gas. Nitrate are anaerobically reduced by bacteria into nitrogen gas.
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135 Gallon Fresh Water Preditor (Monster Fish) tank : Features details on when we switched the 135 Gallon Fresh Water Aquarium to Swimming Pool Filter Sand.
