GE Silicone I CLEAR Summary While not specifically for use in aquariums, GE Silicone I is often used around the hobby as a sealant, both for tanks, cracks, and a general hold all. It is easy to use, and, in my experience, highly effective. While the back label does read "Not for use below the water line, where FDA compliance is necessary, or for in Aquariums" this is to meet legal requirements and remove them from liability. GE Silicone I is 100% silicone and available in hardware stores. It is safe to use in aquariums because of its lack of a mold/mildew resistant agent, which may be harmful to fish. GE Silicone II contains chemicals to resist mold and mildew. It comes in a tube similar to caulking tubes. . How long have you owned this product? I have owned this product for 6 weeks Ease of Use This product was easy and simple to use. Keep in mind you will need to poke the tube open after cutting off the tip of the nose. Pros Cheap Readily available Safe for fish Does not shrink Only takes 48 hours to cure Easy to apply Cons Back lists it as not for use in Aquariums out of FDA compliance Can be messy Somewhat challenging to open Rating Use one of these three emoticons to rate the product in a simple visual way. Please only use the emoticons shown below. Would recommend Please note, I am not liable if this product does not work in your aquarium. I am recommending it based on my individual experience.