It most likely will never be. Low levels are normally found in sea water even naturally. However anything higher than 2 to 3mg/l will contribute to more algae ( the diatom kind). The only way that I know of really to decrease silicates is with using only ro water.
i don't believe these are overly harmful to corals, and certainly not to fish.
PLease note this my UNDERSTANDING of this. This reply is based on something a read quite some time ago and while I believe it to be accurate (or else i wouldn't have posted) if you are REALLY concerned I would look it up somewhere.