Crushed coral has a higher density than aragonite and calcium carbonate. It therefore does not bind other carbonates like phosphate etc as easily. OK to use fine CC IMO.
completely agree, and agree with Crispin re the shape of the particle
IMarine, my appologies.
I have been doing some research into silicates or more importantly what is referred to as soluable silicate. I stand corrected in that there is evidence to show that certain silicates can under certain circumstances become soluable. the article that i am reading at the moment suggests that silicates in the order of 1 to 5 ppm may be disolved out of solution from a silicate based playsand mix although these numbers are not specific to south african silicate sand sources and in addition are related more to the impurities in a silicate sand than the silica itself, indeed no distinction is made between whether the silica in solution relates to the impurities or the silica.
This particular article argues that there is a case for dosing silicates into a marine system, but that the irratic generation / variability of the soluable silica generated from silica sand is not a sufficient source for the marine creatures requiring soluable silica, and the author advocates additional silica dosing.
I will endevor to continue researching this phenominon and report back when i have some more information.
To date i remain unconvinced that silica sand is bad for a marine tank, indeed if one accepts that a certain amount of soluable silica is desirable for organisms (aside from diatoms of course) and that while variable, silica sand does supply this then there is a distinct argument that silica sand is one of the better gravels to use. As an interesting fact, Aragonie also leaches detectable amounts of soluable silica.... but at a much lower concentration than silica sand (about half to be exact) and again as a result of impurities within the aragonite.
I will also be looking into the rates at which the available soluable silica disolves. it APPEARS from my research that the silicate that can be disolved into water (i.e. the soluable silicate) will do so in a matter of days or weeks at the most, and in addition, organisms in the tank (NOT exclusively diatoms) will use this silicate up in an equally speedy fashion. thus there is an argument that putting silica sand into water and replacing the water once a week for 2 or 3 weeks would see the vast majority of the soluable silica removed from the sand (although this is simply a hypothesis at this stage)
I have 3 or 4 different articles which i will be reading and re-reading and will make a thread about this when i feel i understand it fully.
