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Anonymous

Guest
After seeing the article in the library http://www.reefs.org/library/article/r_toonen9.html I am very interested to hear some more opinions. Is it possible to construct a deep sand bed out of silica sand, or at least partially out of silica sand? I have used silica sand in freshwater aquariums before to keep sand-dwelling Lake Tanganyikan fish and have a lot of very fine sand sitting at home. Has annyone else tried this?
Tom
 
A

Anonymous

Guest
There are a few people on this BB have tank with silica sand. Tey reported no problem. Maybe they will post on this thread.
I have sand from Corpus Christi bay in my tank. 5 inches of fine sand estimated about 50% silica and 50% fine crused bivales shells from the look of it. My tankis doing OK without problem. I just need to add Ca and Bicarbonate, and carbonate to it like any other tank.

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Minh Nguyen
Visit my reef at:
http://sites.netscape.net/austinnguyen/homepage
 
A

Anonymous

Guest
Rob's comments on silica sand are based on completely unsound chemistry. Silica sand may or may not be OK, but not for the reasons that he gives.

FWIW, some people apparently have no problem with silica sand, while others have had big problems that went away on getting rid of that type of sand. I expect that its the same as any other nutrient. Some tanks get algae problems with a given nutrient level, and others do not. The reasons for the differences are not well understood (IMO).

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Randy Holmes-Farley
 
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Anonymous

Guest
Randy,
From what I could tell from the article, the basic premise is that silica sand is basically insoluble in water. He gives results from areas with silica sand vs carbonate sand and no difference in the actual silicate content of the water.
Is he wrong in stating that silica sand is insoluble in water? I realize the silica sand = glass may be a strech, but even he states that he isn't sure of the chemical process for melting the sand.
Oh well, just looking for more trivial knowledge.

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Always get a second opinion (and a 3rd, 4th, etc...)
Check out my new homepage padens.homepage.com
 
A

Anonymous

Guest
I have 4 tanks set up in my house one of my tanks has sand from GALVESTON TX. I was just messing around with it and it has been one of my best tanks. I was told by many people I was crazy for putting it in my tank but well I am crazy with one A+ tank. I did try river bed sand once and it was a total mess!! Good luck let me know what happens?
 
A

Anonymous

Guest
Yes, he's wrong in stating that silica is insoluble in water. I believe his reference there was the MSDS (Material safety data sheet) for sand. The MSDS for calcium carbonate says the same thing (which we know, of course, isn't true).

Likewise, the calcium content of seawater is the same near areas of CaCO3 sand, and areas of silica sand. But again, CaCO3 is known to be soluble.

The problem is that some of the ideas in his post seem believable on the surface, but in reality either aren't true, or aren't demonstrated by the "facts" that he provides. I posted a long list of these issues a while back, but can't locate an archived copy at the moment.

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Randy Holmes-Farley


[This message has been edited by Randy Holmes-Farley (edited 13 June 2000).]
 
A

Anonymous

Guest
Reptilicus,

My first plenum system was based on Bob Gomens “Natural Nitrate Reduction Method” and featured 4” of fine silica sand. I used regular silica sand blasting sand, (Texblast) similar in particle size to play box sand. (~0.5mm)

I never had any silica-related problems. The only nuisance algae problem that I had in that tank was a form of macro algae that came with the Marshal Island live rock. I did use X-silicate in the sump, but I am not sure that this was necessary.

Today, I use fine aragonite sands, because of the additional buffering benefit, but for my earlier “test case of one” silica based system, all I can say is “It worked for me”

However, if you can get the Home Depot “Southdown Tropical Play Sand”, it is as cheep as ordinary silica sand.

Regards,

Scott
 
A

Anonymous

Guest
"...his post seem believable on the surface, but in reality either aren't true, or aren't demonstrated by the "facts" that he provides..."

Fine. Post your info, and I'll take a look. I'm quite sure I can figure out what is 'reality' on my own.
wink.gif


-S

R - still adding silica? Did you ever find out if your sponge is a silica/demosponge animal?

[This message has been edited by Steve Richardson (edited 13 June 2000).]
 
A

Anonymous

Guest
Randy

I have the CRC handbook of CHem/Physics in front of me. ALL Silicon oxides are listed as insoluble. This is NOT true of Aragonite, it is listed as having a finite solubility in water. I have to admit I find NO unsound chemistry in Rob's work. Granted I am a Physical chemist and not an inorganic one, but what did you see as unsound? Did I overlook something?
 
A

Anonymous

Guest
Personally, I'd be interested in seeing that list as well, Randy. I am not a chemist, and have never claimed to be, so I won't be offended if you want to correct my chemistry. Craig Bingham, on the other hand is an outstanding chemist, and has an article with conclusions similar to mine (in fact Craig advocates adding silica to reef tanks, and supplements his own). His article ought to be added to his homepage soon.

He sent me an Email making a correction to my discussion of silica chemistry as soon as I posted that article and told that the folks in the glasshop had given me bad info:
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
In particular, I think that the guys in the glass shop gave you some bad information on the composition of glass. There are a huge number of "glasses" and the term refers to supercooled liquids where the viscosity has become high enough for them to be mistaken for solids. It is possible to make glasses out of many things... "cotton candy" is a glass, for instance. Of course the majority of what most people would call glass does have a substantial silicon dioxide content.
But most of those materials are not just melted silicon dioxide sand. Almost all of them have other solids dissolved in the "melt" that alter its physical properties. For example, most glass that is used by humans is soda lime glass. It has sodium oxide and calcium oxide dissolved in
the melt. They lower the softening point for one thing, and make the melt easier to work with. They also make the supercooled melt more soluble in water. So even though diatoms can fairly easily pry silicic acid or
silicate out of glass aquarium walls, that doesn't mean they are as successful at prying silicate out of quartz grains. It can be done, but quartz is the ultimate hard case for silica-loving animals. So I think
that the guys in the glass shop at UC Davis mislead you to some degree. Most glass that you encounter in the aquarium world has is 2/3-3/4 SiO2. The rest of it is other substances. Within the context of your original argument (that silica sand isn't nearly as bad as some people make it out
to be) this little chemical factoid actually strengthens your case. <HR></BLOCKQUOTE>

To answer your question simply, Tom, it can be done, and many people do it. There are potential advantages to using carbonate sands, and if available I use them, but I have (and still do) used quartz sands in the past, and they can function perfectly well for a sandbed where oolitic carbonate sands are unavailable...

Rob
 
A

Anonymous

Guest
I'm presently running 3 tanks with all silica sand with no problems ( and yes this is the cheap commercial grade sand ). My first SW tank in 1965 was silica sand, because that's all that was available at the time. My sand beds are about 3 1/2" deep with plenty of live sand critters, worms, etc. I've never had any algae problems with these types of tanks.
Regards,
David Mohr
 
A

Anonymous

Guest
Rob:

More than happy to oblige. Let me first point out that I too add silica to my system on a daily basis, so I'm not a silica-phobe! I'll put together to comments in the next day or two.

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Randy Holmes-Farley
 
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Anonymous

Guest
Microreefer:

Well, the 77th edition of the CRC handbook lists aragonite as "i", or insoluble on p. 4-48. I don't know what edition you have or where you are looking. Nevertheless, the solubility of SiO2 is about 120 ppm. I'll post all my chemistry concerns in a few minutes.

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Randy Holmes-Farley
 
A

Anonymous

Guest
Rob:

First, I agree with you on several points, including the fact that people can have silica sand beds without diatom blooms. If you keep other nutrients low, diatoms may never be an issue, even in high silica tanks. I also agree that the benefits of aragonite are overblown, though I do use it.

I think, however, that the evidence that you supply is not convincing that people never get diatom blooms due to silica sand. Maybe they do, maybe they don’t. I’m not expressing an opinion on that question, just your evidence on whether it is possible or not.

Many tanks have high nitrate, phosphate, and organic levels. Some get green algae growth, others do not. Some get diatom growth, others do not. None of us really knows why in every case. I’m not convinced that such people won’t have diatom problems if silica is high, or if they have a lot of silica sand.

A line by line commentary:

“Quartz (SiO2) is considered “totally insoluble” in water according to the US MSDS,...”

Here are two references that give the silica solubility in pure water at 25 deg C and pH 8 to be 120 ppm.
http://osmonics.com/products/Page696.htm http://www.gc3.com/techdb/manual/depotext.htm

For purposes of an MSDS sheet, that’s probably close enough to insoluble. I’ve written MSDS sheets, and I might give that same description for use in a safety brochure. Does that mean that if I put 120 mg in a liter of water that it will immediately dissolve? No. It means that in the long term, it will, but that in the short term it may be kinetically limited. If I put a pound of finely divided SiO2 in a liter of water, it will approach the solubility much faster. How fast? I don’t know. It may be fast enough to be important, and it may not. Without kinetic data one way or the other, we cannot conclude whether dissolution of sand can be important to a reef tank or not. This point is also important in comparing sand to glass walls (below).

Further, the oceans are undersaturated everywhere with respect to silica according to “Chemical Oceanography” by Frank Millero (p. 300). Thus, there is the driving force, if not the kinetic pathway, for silica to dissolve in seawater.

“The fact is that quartz sand (and the walls of our aquarium and even the silicone rubber which is the most soluble of the lot) do not dissolve in seawater to be measurable”

First, silicone rubber itself contains no silica (maybe you know that; your sentence seems to imply that it contains silica, but that may be a misinterpretation on my part). Some silicones may have some added silica as a stiffener, but many do not. Second, silicone sealants are crosslinked polymers, and as such have zero solubility in any solvent (though trace impurities of other things in them may dissolve). Here’s a link that talks about silicones:
http://www.pbs.org/wgbh/pages/frontline/implants/corp/history.html

So, on to the point that the walls of the aquarium do not dissolve. How do you know that they do not? By measuring silica in the water? No. I’ve been making daily additions of silica to my tank (as highly soluble sodium silicate; equivalent to 0.02 ppm SiO2 every day) since October and none has ever become detectable with a Hach kit. Why? Presumably because tank creatures use it up as fast as I add it. The same could be true of silica from the walls, and from the sand. It is also true in the oceans, where diatoms use it up as fast as it is added. Silica effluent in rivers often doesn’t even make it to the ocean because it is consumed by diatoms in the estuary (again, according to Millero).

By not seeing the glass dissolve? No. To bring a 90 gallon tank from zero ppm silica to 0.2 ppm silica (which is the approximate NSW surface concentration), would only require 10 nanometers of the surface glass to dissolve. That’s only about 100 atoms. How can you tell that that hasn’t happened?

“you would expect to see big differences in the silica concentration around sandy beaches”

Why? The silica concentration in seawater is controlled by the growth of organisms. If diatoms drive the silica down to the level that they can no longer adequately draw it from solution (which they do, driving it down to less than 0.2 ppm), then the amount being added will not impact the concentration. It could impact the diatom concentration, if in fact dissolution of beaches were a significant addition to the ocean. I haven’t seen data on diatom concentrations comparing calcerous coasts to silica coasts. Perhaps you have that info.

“(roughly 2 ppm everywhere other than adjacent to the mouths of rivers...”

In Millero’s book, the ocean surface silica concentration is shown to be much lower in surface waters across most of the globe. More like 0.2 ppm. Do you have different information? He also shows that the silica concentration increases greatly as you go deeper, where diatoms are not using it up, and in fact dead, sinking diatoms are dissolving (giving it a nutrient type profile). Thus, the amount of silica that would have to dissolve to give NSW levels of silica in a tank is quite small.

“If it doesn’t make a difference on a global scale, how much difference do you think it can make in our tanks?”

Well, I’d argue that it could be huge. First, the amount of sand in a tank is vastly greater per amount of water than in the ocean. By a factor of what, a thousand? a million? More? So a little dissolution goes a long way in a tank, but nowhere in the ocean.

Second, the amount of sand per diatom may be vastly higher in our tanks than in the ocean (for the same reason). Third, since tanks don’t have river inputs or hydrothermal vents, other inputs, such as sand dissolution, may become the limiting factors.

“given that, it’s pretty hard to argue that using quartz sand is bad when the glass box that your putting it into is made of the same stuff.”

Well, ignoring Craig’s comments that it may not be the same, I don’t find it hard to argue at all. Based on the known solubility of silica, and the fact that it doesn’t immediately dissolve to reach that solubility, we must conclude that the dissolution is kinetically limited. Dissolution of solids, when slow, is typically limited by surface area (among other things). Rock candy and jaw breakers, for example dissolve a lot more slowly than a spoonful of sugar in your mouth.

The surface area in a sand bed is far, far higher than the glass walls of an aquarium (I calculated it once). Thus, the dissolution of a sand bed could be orders of magnitude greater than the walls of the aquarium.

So can we conclude that since a little of something is OK, that 10, or 100 or 1000 times as much is also necessarily OK? It might or might not. You likely would not say that about limewater, or iodine, or strontium, etc.. Why say it about silica?


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Randy Holmes-Farley
 
A

Anonymous

Guest
Randy,

Now this IS interesting! I have the 61st edition of the CRC handbook and on page B-87 it lists aragonite as soluble .00153 g/100cc in cold water and .0019 g.100cc hot water. This same table lists all silicon oxides as insoluble in both hot and cold water (page B-143). If CRC changes it's mine, who are we to trust????


ARRRGGHHH!
 
A

Anonymous

Guest
Randy I just want to emphasize the beginning of your post again because people have already misinterpreted your main point when summarizing this in other places <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote
I agree with you on several points, including the fact that people can have silica sand beds without diatom blooms. If you keep other nutrients low, diatoms may never be an issue, even in high silica tanks. I also agree that the benefits of aragonite are overblown, though I do use it.
OK, having re-emphasized that as the basis of this discussion, I think that you make some good points Randy, and it is obvious that my careless oversimplification of a number of points has impeded communication. As far as I can tell from your post here, we are in complete agreement about most issues. The main point that I wa strying to make in that post was that the concern over the addition of a little silica to reef aquarium water was unjustified, and that the dissolution of silica sand was largely equivalent to the dissolution of the walls of the aquarium, at least in terms of the need for concern among aquarists (your point about surface area is well-taken and I agree completely). I agree that the discussion can get a lot more complicated and the exact composition of the sand matters a great deal (e.g., diatomaceous earth -- diatom frustules -- would be a very bad inclusion in the sandbed), while I have essentially used silicon dioxide, quartz and biogenic opal interchangably, but I don't think that changes the primary point that I was trying to make. I would still argue that quartz is negligibly soluble in seawater compared to a hydrated form of silicon dioxide and that the addition of a silica sandbed is unlikely to have any measurable effect on the concentration of silica in aquarium water. In fact, depending on the source of the aragonite added to an aquarium, a carbonate bed with a reasonable inclusion of biogenic opal (in the form of ancient diatom frustules and sponge spicules, etc.) could well provide more available silicic acid to the system than would a really clean, crystalline quartz substrate...

Whether or not we agree on the specifics of how we get to the conclusion, the bottom line from Craig's work, and our exchange here is that people ought to be far less concerned about the complete elimination of silicate in their tank water. Obviously you and Craig both agree with that point given that you actively supplement a highly solubale form of silicate into your reef tanks, and I agree. I argue that the addition of a pure crystalline quartz sand substrate to an aquarium ought to have little or no noticable effect for the average aquarist on the growth rates of silica-loving animals, whether the concern over diatom growth is justified or not.
Given our agreement that silica is not the demon it is made out to be, and Craig's addition that the walls of our aquarium are greatly more soluble than are quartz sandbeds, I am simply trying to rebut the myth that the addition of quartz sands to a reef tank will release substantial amount of silicate into the aquarium water and result in disasterous effects for the average reef keeper. This is not historically the case, and when the first recorded coral aquaria (at least for which I could find a record) were established around 1900, they used exclusively quartz sand, and were amazingly successful for the time period (some people actually succeeded in spawning and growing captive-raised corals in these tanks without any modern equipment such as lights or pumps!). This myth that the addition of silica sands will cause a diatom bloom of such dramatic proportions that it will prevent establishment of a reef aquarium started and propagated in the hobby trade recently (about the time carbonate sands became commercially available at 10-50 times the cost, hmm...), and I am simply trying to explain that silicate is not a nutrient that needs to be eliminated at any cost from an aquarium, and people who do not have access to the fine carbonate sands widely sold in the US can still establish and run an effective sandbed...

Rob
 

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