GARF's "Bullet Proof Reef" Anyone?

[rkelman]

As far as I know there is no Silica in Cement..

[Aleks]

Originally Posted by rkelman

As far as I know there is no Silica in Cement..

I think in most cement mixes there is silica....like around 0.5-1%?

[soapy]

Here follows a little excerpt from here: http://www.azom.com/details.asp?articleID=1317

>>>>>When water is mixed with Portland cement a complicated set of reactions is initiated. The main strength giving compounds are the calcium silicates which react with water to produce a calcium silicate hydrate gel (C-S-H gel) which provides the strength, and calcium hydroxide which contributes to the alkalinity of the cement. Tricalcium silicate reacts quickly to provide high, early strengths while the reaction of dicalcium silicate is far slower, continuing, in some cases, for many years. The other cement compound of particular relevance to steel reinforced concrete is tricalcium aluminate. It reacts rapidly with water to produce calcium aluminate hydrates.<<<<

[Jack]

http://www.youtube.com/user/smorell82689

[midgetwaiter]

I don't think that silica in rocks or substrate is necessarily a problem. I've used silica sand before without issues and if you think about it some silica compounds obviously don't dissolve readily or the whole glass thing would be an issue.

These was an article by Randy Holmes Farley a while back, I think in Advanced Aquarist, that looked at using silica based substrates. My memory of it is cloudy but he found that some sands contained higher amounts of silica compounds that could dissolve than others.

It seems reasonable that the same would be true with cement.

[soapy]

Yes I am pretty sure that the silica bound up in the crystalline structure of glass and sand is a different animal than the kind in suspension or cement. Here are the results of the silicate tests I took at the time of my aragocrete project:

RO water .25 PPM
tap water .5 PPM
tank water with aragocrete 2 PPM & above

note that 2 PPM is the upper limit of the test, so god knows how much silica was in that water.

I didn't test the water after yanking the aragocrete and haven't tested lately but as soon as the cement came out the diatom bloom died off. I will make some more tests soon and see for sure what was going on. I haven't given up on aragocrete yet anyway and think it is good idea.

[new but handy]

I made about 100 lbs of rock with cement. I don't have a diatom problem or any other problem. I made my rock in about march last year and I did weekly(ish) water changes in a rubber made bin in my yard. I fired up my tank in sept.