I've been researching different Silcone products for the sealing, here are the ones so far that sound decent. But i don't know that well which would be good for an aquarium/PC, so drop me aline of suggestions

HOME DEPOT

GE 2.8 oz. Clear Silicone Tub and Tile Caulk
Model GE284 3TG
Permanently flexible, mildew-resistant 100% silicone sealant adheres to tile, porcelain, glass, fiberglass, marble, wood, stainless, aluminum and most plastics. Lifetime satisfaction guarantee. Won't crack, chip, peel, or dry out. Easy to use squeeze tube.
Store SKU # 469301
Internet # 107708
Catalog # 100004845     
Price: $2.99/ea

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CANADIAN TIRE

XST Paintable Silicone Sealant 
Price $7.89

eXtreme Silicone Technology
Uses advanced silicone technology to make this the best sealant available today
Offers premium silicone performance plus paintability, and XST cleans up with soap and water
Permanently flexible
Won't shrink or crack
Low odour formula
Use on: windows, doors, moulding, baseboards, painted surfaces, siding and trim, drywall 
 
 
HOME HARDWARE

Weather Shield 3 Pack Silicone Seal Bonds to porcelain, glass, marble, fiberglass and many other materials. White or clear. 300 mL.
2034-408/444