OK Steve.......Sorry to post this. I just did about 45 minutes researching this silicone stuff.....Here is a post I found.
Thought I'd just add my experiences with silicone.
I was VERY unluckly when buying tanks for my fish house. The first batch of tanks (20 or so) were purchased from a very respected local manufacturer, my step-father also purchased a large tank too. He was first to set up and stock his tank..... all fish died within 24 hours of putting in the tank. The usual tests/self doubt/fish and water supplier blame etc followed, I then loaned him a batch of my juv angelfish...these too were dead in 24 hrs. After eliminating all decor and usuing aged water from one of my mature tanks and finding the problem was still there it was evident the tank was the problem. We contacted the supplier (and checked my new tanks) to find that he had problems with much of his new stock. His sealent supplier had sent him a batch of sealer that had had fungicide added, it was clear and behaved like 'aquarium grade' so couldn't be detected until used. Needless to say we were compensated. 12 months after this I went to another supplier to buy the second half of my tanks only for the same thing to happen !!!! I knew the syptoms the fish showed was poisoning, I contacted the manufacturer straight away but he didn't believe me until the questions and complaints started to pour in. It almost finished him, needless to say he appologised and my tanks replaced.
This was 15 years ago, regulations may be tougher now, and chemicals handled more responsibly, but I am very cautious when using any type of sealer. White almost always contains anti mould/fungus chems which are VERY toxic. I have used a black sealer but bought it from an aquarium manufacturer (I have a bit more faith now ). I would avoid any bathroom sealer.
The symptoms fish show are:- Staying to the sided of the tank, they never venture into the middle ; heavy breathing ; 'glazed' expression ; listlessness ; death within 24/36 hours.
Looks like you may have an issue with using that silicone with the mold and mildew preventer in it. MAN DOES THAT SUCK!!!!!!!
I read a great deal about some kind of stuff you can get from Canadian Tire....I think you are in Canada so you should know what I am talking about. Good luck to you and sorry.......