The stuff you have is definitely not safe. Many aquarium safe brands of silicone don't say so on the label. Some even say "not intended for prolonged underwater use." Ha. Those which explicitly say so usually cost at least twice as much (jerks.)
GE and DAP both make good cheap brands. Usually marked "window and door." Avoid anything for the bathroom or kitchen. Make sure it's silicone II, not I, although sometimes even this is not specified.
NO latex, nothing benzyl or diazolidinyl, phthalates, CaCO3, etc. I suppose inert whiteners/opacifiers like titanium dioxide are OK but what's the point unless you want it white.
Another tip-off for safety is "food safe." If it's 100% silicone and you can find "ASTM Specification C 920, Class 25, Type S, Grade NS" on the label, you're good to go.