You already said what you don't want in it.. the anti mold/mildew additives. While I've heard people say they've used it with no issues, it's just not something I would ever do. Those chemicals can leech out of the silicone and kill your fish. Your best bet is to start over using silicone with no additives. I think it's GE I for doors/windows that is safe, but you'll still want to make sure it makes no mention of mold/mildew inhibitors.
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