I used Tec7 (widely available in Europe, not sure about US) recently on a project. It's a translucent silicon, rated safe for fish, and you can apply it underwater. I must admit, I thought the guy in the DIY store was messing me about when he said you can apply it underwater - but it worked perfectly.
I have used GE SCS 1203 (black) silicone while resealing my 150gal and my 200gal. I have had them running for about 6 and 11 months now without an issue. They come in tubes and it took me roughly 1.5 tubes for the 150gal and 1.75 tubes for the 200gal "I do put mine on a little thick and let it cure a couple extra days before adding water. I would highly recommend this brand.