Wait until the silicone has fully had time to cure. The outside may be dry but the inner part may still be wet. Give it a full 24 hours, 48 is better. One thing I have found, sometimes silicone will not stick to old silicone. You may have to remove all the silicone and reseal the whole tank. Hopefully you wont, but dont be surprised if you do. Fill the tank somewhere that wont get damaged of the sealant doesnt hold and let it sit for 24 hours before bringing it into the house.
Check your silicone. Make sure it doesnt have any colorings, mildew inhibitors or anything else added to it. Use something like GE Type I 100% pure silicone only. Dont use Type II or the kitchen/bath types.
Why do I love fish? Because every time I stare into the little world I have created for them, every problem I have just floats away....