Sand - composition and effect

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For those using silica (playsand) or beachsand i found this a great explanation of the available substrate choices and the implications



Mods This is an exert from a article from REEFKEEPING.COM written by Tom Murphy. If there should be any copy right implications please delete.



Mr. Sandman, Bring Me a Dream
When using all live sand there is no problem setting up the tank, well, except the cost. Many reefkeepers feel it is a little too steep. The usual solution has been to use base sand (dead sand) and mix it with live sand. This method does work pretty well and, in years gone by, there was Southdown Tropical Play Sand to the rescue. Why Southdown? Well, true live sand is actually a mineral called aragonite. It is composed of calcium carbonate composed mainly of shells and skeletons of dying reef creatures over hundreds or thousands of years. The advantage of aragonite is that it not very dense (specific gravity ~2.94), lacks sharp edges and has buffering capability (can neutralize acids). Since it very abundant and natural to the reef environment, it is perfect as base sand. That was the wonder of Southdown; it was pure aragonite and available at the hardware store for under $10 for a 50 pound bag. It was perfect - and then they stopped marketing it. It is so rare today that threads continually pop up citing appearances that, like UFO’s, are never confirmed.
You can still buy aragonite sand but usually only at the local fish store (LFS). It does cost a lot more than Southdown, but it is still true aragonite. “Live sand” in bags, also sold at the LFS, is something to avoid, however. It is just a bag of dead aragonite, with some nutrient solution added, and a few cultured bacteria. It’s artificial from the word “GO” and lacks all those tiny, sand-shifting organisms so important to a great deep sand bed. It is rarely worth the extra money.
The question arises, “If cheap aragonite is not available, can other sands be used?” The answer is yes. While not as perfect for your tank as true aragonite, they too can be used as base sand. First off, it must have the proper size, in the range of 0.05-2.0 mm. The majority of the particles should fall in the range of 0.15 through 0.25 mm; about the same size as fine-grained, granular sugar. Some, not all, silica sands can be found that meet these criteria. Usually that will be found in silica play sand or sand box sand. The major drawback is they are denser and have relatively sharp edges. They also offer no buffering ability at all.
Let me talk a bit about buffering. Once oxygen is depleted in the bed, anaerobic organisms appear. These guys process the food they consume mainly by using fermentation - “Cheers!” Yes, they do make alcohol but carry it out too far. You end up with organic acids, like vinegar, a completed fermentation by-product. Now, pour some vinegar over aragonite and it fizzes like an Alka-Seltzer. This is because the acid, vinegar, reacts with the base, calcium carbonate, and produces a neutral salt - calcium acetate. The net result is that some sand dissolves but the acid is neutralized.
There is a side effect, however. The reaction also produces free carbon dioxide that, dissolved in water, produces a weak acid, carbonic. In a perfect world this would reduce the bed’s pH below 6.5 where the carbonic acid reacts with the calcium carbonate in the aragonite forming calcium bicarbonate; a very good thing as it adds calcium into the water column.
Alas, it is not a perfect world. In the days of yore it was claimed that having a deep sand bed was the way to go as it provided all the calcium a tank would need. Sadly, this is not the case and having a deep sand bed is not the road to having a calcium-dominated tank. Only a small extent of the sand bed meets these conditions and the amount of calcium dissolved will nowhere meet the calcium requirements of most hobbyists’ tank. Yet, I’m always the optimist and, even though small in its contributions, every bit helps.
Notwithstanding, silica sand does work. It was once thought that silica sand would release untold amounts of silicates into the water column, thereby fostering a continual diatom outbreak. Sand is a major component of the glass in your tank, and if it dissolved, be prepared for a flood even Noah can’t endure! Silica sand is inert.
 

viper357

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He's basically just saying what we already know, isn't he? That aragonite is not a feasible means of maintaining calcium in our tanks and nor is playsand. Also that playsand/silica sand does not cause diatoms.

If there should be any copyright implications please delete.
A link to the original article will solve that issue.
 
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Who is Tom Murphy? How can you compare silicates in the sand compared to the glass that has been treated and processed. What studies has he done on this for reference?
 
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Hennie that is a great thread and DLSB is 100% fantastic, but I think the discussion here goes aroung silicate sand and aragonite and which of the 2 is beneficial. Would you say it is OK to add silicate sand to your system as per the indication or would you rather use silicate sand as the author has indicated that it has no negative effects?
 
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Hennie that is a great thread and DLSB is 100% fantastic, but I think the discussion here goes aroung silicate sand and aragonite and which of the 2 is beneficial. Would you say it is OK to add silicate sand to your system as per the indication or would you rather use silicate sand as the author has indicated that it has no negative effects?
Great thread Hennie. Would also like an opinion on Alfie's observations. Thanks Alfie. Yes... composition and effect. And the question that needs answering relate to effect. They both do the job. But what are the positive effects of one over the other, if any.

PS The author does not subscribe to silicate. He merely points out that silicate is inert
 
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Notwithstanding, silica sand does work. It was once thought that silica sand would release untold amounts of silicates into the water column, thereby fostering a continual diatom outbreak. Sand is a major component of the glass in your tank, and if it dissolved, be prepared for a flood even Noah can’t endure! Silica sand is inert.[/quote]

Though he says it it is inert he is questioning the release of silicates as indicated and I would like to know if this is or is not the case as he is comparing it to the glass.
 
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Inert it is. Or certainly in the space occupied by our lifetimes. The chemistry of silicone is almost as diverse as carbon. However Siloxanes on the other hand is a group of silicone's that IMO could be the culprits of unexplained algae issues.
 
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I think the discussion here goes aroung silicate sand and aragonite and which of the 2 is beneficial. Would you say it is OK to add silicate sand to your system
In short, YES - you can safely add silica sand to your system. Let me elaborate a bit...

The 'aragonite sand is the best' statement has been hijacked by the advertising people, and is really a sales gimmick, in my humble opinion. Although aragonite does release some calcium at our tanks' pH levels (albeit quite a small amount...), this is it's only advantage over silica sand. The sand gradation (particle size distribution) is a much more important aspect to the success of our tanks than the addition of a small amount of calcium, which can easily be added by some other means.

Here are a few extracts from an excellent article by Dr. Ron Shimek Ph.D, published in Reefkeeping online magazine: How Sandbeds REALLY Work by Ronald L. Shimek, Ph.D. - Reefkeeping.com

Sands surrounding natural coral reefs may be made of a number of substances. Around volcanic islands there are often regions of volcanic lava sand. Volcanic islands are the basis for most coral atolls and many fringing reefs, so lava sands are commonly found around reefs in nature. Coral reefs located near areas of river mouths or extensive areas of runoff often are surrounded by silica sands or fine sediments of other upland or inland sources. Of course, coral reefs may be surrounded by calcareous sands resulting from the breakdown of corals and other calcifying organisms. Calcareous sands may also be formed by the precipitation of particulate calcium carbonate in coral lagoons, one of the natural sources of oolitic sand. Calcareous sands may also be formed from the skeletal breakdown of other organisms, such as foraminiferans, bivalves, calcifying algae, or barnacles.
The chemical composition of the sands has a small effect on the organisms found in the sands, but that effect is minor compared to the effects due to differences in sediment particle size distribution. The sediment particles found in any given area are primarily due to the effects of sediment movements caused by wave action and water currents. Sediment density has some effect on what is present, but basically for any given sediment, finer particles will be found in areas with less water movement. Consequently, the pattern of sediments surrounding a coral islet that is one part of a coral atoll will be a complex tapestry of sediment sizes. In general, coarser sediments will be found in areas of higher current flow and wave action while finer sediments will predominate in areas of less kinetic energy. The absolute position of the sediments will often vary from season to season, particularly in intertidal and shallow subtidal areas.
The size distribution of sediments in any marine soft sediment area is critical to the determination of the organisms living in those sediments. Organisms live on, and between sand grains, and the mixture of the sizes of the grains is critical. Sand grains of inappropriate sizes may be too big to move or, conversely, too small to be stable. Additionally, the mixture of the various sizes determines the ease with which water moves through the sediments.
The functionality of these sediment layers, in the context of either the aquarium or natural ecosystem, is dependent upon the diversity and richness of organisms in the sediments, and this is directly related to the sediment particle distributions that were mentioned previously. Well sorted sediments with a narrow particle size range, are generally quite optimal for a few organisms, primarily those adapted to that particle size range. For everybody else, well… they don't work so well. In aquaria, where the maximum diversity and richness is required, the aquarist needs to ensure that the sediment particle size range is fairly large. Of course, "fairly large" is a matter of opinion. Marine benthic ecologists and other folks that study sediments categorize sediments in a series of sizes based on the negative logarithm to the base 2 of the size. Sounds pretty complicated, but really isn't. What this means is that starting with the upper sand limit of four millimeters in diameter, the sand size categories are: 2 mm to 1 mm, 1 mm to 0.5 mm, 0.5 mm to 0.25 mm, 0.25 mm to 0.125 mm, and 0.125 mm to 0.063 mm.

For a sand bed to contain the most animals of the most species, it really should have a distribution where sediment sizes span from about 2 mm to 0.063 mm (2 mm to 1/16th mm), and where most of the particles are in the 0.250 mm to 0.125 mm range. This will make a sediment that is acceptable, if not perfect, for most animals.
I could be wrong, but IME most 'aragonite' and 'crushed coral' sand particles are *much* larger than 0.25mm, and as such make a rather poor substrate for a DLSB. I would much rather lose the questionable benefit of the small calcium addition of aragonite sand, and have a thriving, diversely populated LIVE sand bed.

As for the silica sand releasing silicates into the water which could feed diatoms, let me refer you to an article written some years ago by Dr. Craig Bingman, Ph.D (a rather well known chemist who should know his stuff...), and published in the now defunct Aquarium Frontiers website Aquarium Frontiers Feature:

Silicon belongs to the same group of elements as carbon (see Figure 1) and shares some properties with it. Elemental silicon has no known role in biology. The biologically relevant form is the +4 oxidation state, which in biological systems is almost invariantly covalently bonded to four oxygen atoms that sit at the corners of a tetrahedron around a central silicon atom.

There are a number of variations in the hydration state of these SiO4 centers. In silicic acid, the simplest form, the four corner oxygens are part of hydroxyl groups, giving it a composition of Si(OH)4. Silicic acid is a weak acid. The first deprotonation reaction is half complete at a pH of 9.47, giving Si(OH)3OH-. A second deprotonation reaction is half complete at a pH of 12.6. So, at seawater conditions (pH 8.1 on the oceanographic pH scale), approximately 96 percent of the silicic acid is in the form of Si(OH)4 and four percent is ionized.


The other extreme end of silicate hydration is quartz, SiO2, which could be thought of as completely dehydrated Si(OH)4. Quartz is the least soluble form of silicon found in nature. There are many intermediate hydration forms, which could be described as SiO2(H2O)x, where x varies between 0 (quartz) and 2 (silicic acid.) The biogenic opal formed by diatoms is one example of an amorphous, solid, polymeric form of silicic acid that is more hydrated than quartz, but much less hydrated than free silicic acid. Biogenic opal is substantially more soluble than crystalline quartz.

He concludes his article with the following golden nugget:

If I were to tell you that there is an organism that can help compete with nuisance algae for nutrients, and will allow you to feed your system phytoplankton simply for the cost of rubbing a magnet on the front glass of your tank, you might be willing to pay quite a lot of money to get such a creature established in your system. Because this organism actively reduces nitrates and packages nutrients in easily skimmable (as well as nutritious) packages, you might be willing to pay even more. I’m hopeful you will not be too disappointed to learn that you already have them in your aquarium, nor too sheepish to learn that you have been doing your damnedest to wipe them out. They are none other than your old enemy, diatoms. One sometimes wonders if the minor aquarium gods always know what they are doing, or what implications their choices might have for their aquatic worlds.
Hennie
 

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