I often get asked what silicone is safe to use in a reef tank.  I have personally used three types of silicone with no ill effects at all.  The important thing to consider when selecting a silicone for use in a reef tank is to make sure that it is 100% silicone with no additives to eliminate mildew.  Do NOT use a kitchen or bath silicone. I have never seen a kitchen or bath silicone that does not contain mildew protection.

What silicone brands are reef safe?

The three types of silicone I have found that meet these requirements are:  All Glass Aquarium silicone, GE type I silicone and DAP 100% Silicone Sealant.  Manufacturers tend to change their product names and ingredients, so always verify that the item is 100% silicone with no additives for mildew reduction.

What about long term use?

My 125 gallon reef tank has a 40 gallon sump that was assembled entirely with GE Type I silicone.  My 46 gallon bowfront reef tank was resealed with black DAP 100% silicone sealant.  I have had no ill effects from the use of these products and no problems at all with corals or invertebrates.