I am very sorry for your loss. Exactly what type of silicone did you use? They are not all created equal. Some have mold inhibiting properties, and these are not to be used in aquariums. Whenever you have a situation where something foreign has possibly gotten into your tank, always do a large water change, and run fresh carbon. Carbon loses it's effectiveness and is virtually useless after a week or a little more. I do not use carbon in my tanks, unless I want to clarify the water or something has gotten into my tank that is unwanted. I always keep a large jug on hand and some fine media bags for this purpose.This is not something that would have showed on an ordinary test kit.