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.
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.