From what I can determine by researching labels and product descriptions, GE Silicone II is a line of different silicone products with various additives designed for specific purposes, even though the different formulations are all labeled "100% silicone". GE Silicone I once said specifically on the label that it is safe for aquariums, but years ago they dropped that wording for some reason. (I suspect it is by agreement with other companies that purchase silicone from GE and market it under their brand specifically for aquarium use, but that's just my suspicion.) However, unlike most GE Silicone II products, GE Silicone I does not specify that it is NOT safe for use in aquariums, so judge for yourself or take the word of many aquarists (including myself) who have used it successfully for many decades with no problems.
It's a little late to help you this time, but if you're looking for just enough aquarium-safe silicone for a small project, Loctite markets a squeeze tube that specifically says it's safe for aquarium use. I have bought this at Lowe's, but for some reason, I can't find the same product in a caulking gun size. The small squeeze tube costs nearly as much as a large tube, but I've found that once a caulking gun size tube is unsealed, the clock starts ticking and its useful life is limited before it cures in the tube; plus, the smaller tube is easier to manage on small projects, so unless I'm planning a complete tank build or resealing project, the small tube works fine.
"May the Fish be with you."