The picture you posted shows that the sililcone you bought is mildew resistant. This is bad, it means there are chemicals in it that are meant to kill stuff that tries to grow on it. I would imagine its possible that it could leach into your tank.
There are two types of Silicone I. The tub and tile stuff is mildew resistant, the door and window stuff is not. They are both Silicone I, and they both come in all colors including clear. I would not use the stuff you pictured.