<a href=showthread.php?s=&postid=7657820#post7657820 target=_blank>Originally posted</a> by Travis L. Stevens
I stand corrected with the articles below, but might I add that silica sand does not dissolve an amount that is higher than natural seawater and is actually lower than that of what is found in most of our synthetic salt mixes. In short, the amount that is dissolved is rather neglegable; not "does not leech silica" at all
Here are some articles. The abstracts below are intended to any reader. Not just you, Russ. :thumbsup:
SILICON â€" FOE OR FRIEND? by Craig Bingman, Ph.D.
--This article gives a better understanding of Silicon and Diatoms. It also debunks many myths that are associated with it. It does not mention anything about Silica Sand, but should still be read.
--Silica Sand contains Quartz Crystal (SiO2) and as quoted here: "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." Although Silicic Acid can easily be used by diatoms.
--Just because you may use an RO unit does not mean that you are completely eliminating silicon, diatoms, or both in your aquarium: "So, silicic acid passes through many reverse osmosis (nanofiltration) membranes fairly readily. Some newer membranes have higher rejection rates than older cellulose triacetate (CTA) or thin film composite (TFC) membranes, and they are available on the aquarium market." Luckily an RO/DI unit should eliminate various silicon forms.
--For those that are concerned about keeping specific organisms such as sponges: "Diatoms are the main consumers of silicate in the ocean, followed by sponges and a number of protist groups. Some higher organisms have small requirements for silicon, which will be described later."
--Tap water can be a leading cause of silicon forms and even diatom outbreaks: "“Mean tap water†has a composition similar to “mean river water†and the concentration of silicate in mean river water is about 40 times higher than the silicate concentration in surface seawater in the tropics. So, here is our first problem and one that the aquarium community seems quite familiar with: Some tap water is loaded with silicate and it can certainly promote diatom blooms in reef tanks."
--Because I don't want to take up much time, definitely read all of the topic "Silicon and Aquarium Husbandry" with a main focus on paragraphs 1-4
Silica in Reef Aquariums by Randy Holmes-Farley
--This article does talk about Silica Sand in the Reef Aquarium
--It looks like soluble silica is easily taken care of: "I’ll also show with dosing experiments that soluble silica is rapidly depleted from my reef tank (about 50% per day)."
--Randy did tests on a few different sands and here were his conclusions: "From these experiments, I conclude that: 1. The “silica†play sand that I purchased from Home Depot can substantially raise the dissolved silica concentration in seawater. 2. The dissolvable portion of the silica sand cannot be completely removed by several rinses with either fresh or salt water, although it may be decreased somewhat by that process. 3. Southdown calcium carbonate sand (likely aragonite) can release soluble silica, but about ten fold less than the “silica†sand."
--Here is where a bunch of speculation occurs between aquarists: "Is it OK to use silica sand? Probably. Many people do so. I also believe that not all “silica “ sands will be the same for the reasons described above relating to processing of the sand and the nature of the mineral inclusions present. So the fact that many people successfully use some (or many) types of silica sand does not necessarily imply that all people can use any type of “silica†sand without a problem. "
--Randy dosed soluble silica in his tank and this is his conclusions: "From these experiments, I conclude that: 1. Silica can be a limiting factor for diatom growth in some reef tanks 2. Adding soluble silica can increase diatom growth 3. The increased diatom growth was not apparently in addition to, but in place of, green algae growth 4. Added soluble silica is rapidly depleted from some reef tanks 5. Taken together, these facts suggest that silica supplementation may be desirable."
These two articles show that, yes, silica sand can leech soluble silica back into the aquarium, but not at a concentration higher than natural sea water. It also shows that silica is quickly and easily consumed by marine organisms and their sacrifice feeds other marine organisms or is readily skimmed out. Silica dosing is recommended by Randy Holmes-Farley. The dosage amount of silica is close to that of what is dissolved out of the silica sand. Silica is already in our tap water, can be in our RO water, is most likely not in our RO/DI water, and is even in our synthetic salt mixes. One illustrations shows that RC (assumed to be Reef Crystals) is actually far above natural seawater in soluble and insoluble silica. It is believed that not all silica sands will dissolve the same amount of silica. Diatoms are a large consumer of silica, but most herbivorous snails actually consume diatoms and so should readily be controllable if sufficient thought and planning is taken.
In short, Silica Sand is safe to use, but your milage may vary. In my opinion, using a silica sand most likely can add an extra "cycle" in a reef tank. Almost all new reef tanks go through the nitrogen cycle, a cyanobacteria cycle, and an algae cycle. Adding silica sand just might add a diatom cycle if there aren't enough organisms to compete with diatoms
