Next came the installation of the window. I chose acrylic over glass for my window, based on weight, cost, clarity, and personal preference. I've owned several acrylic tanks, and I've never had any trouble with them scratching if I was careful. After doing alot of research (and a bit of math) I decided to go with 1.5" cast acrylic. 1.5" is probably a little thick than necessary (so is the rest of the tank) but I was able to buy it for a good price, and felt more comfortable with the added strength given by the extra thickness (again same story with the rest of the tank, over built).

The window would be installed using silicone as a gasket. The silicone itself would not hold the window in place, or add any strength to the tank, as silicone does not really bond to acrylic. I would rely on water pressure alone to hold the window in place. Choosing a silicone was no easy task either. I really couldn't find much information on what silicone professional aquarium builders use on a tank of this scale. I contacted GE, DAP, and a few others regarding my situation. I found no help there. In fact, when I explained what I planned to them, they all stated (with the exception of DAP) that their product was not intended for use in aquariums.

I found a brand sold by Aquatic Ecosystems, called Star Brite Marine Silicone. They state that this brand is intended for, and safe to use on aquariums, so I decided to use it. I purchased 15 tubes of the silicone from Aquatic Eco.

Before installing the window, I made some "braces" (six) from pvc tubing and fittings. The purpose of these braces would be to span from the window, to the back of the tank and hold the window in place while the silicone cured, and until the tank was full of water. The braces had a threaded union on one end that would allow approx. 1" of adjustment.

When it was finally time to install the window, I lined the tank with used carpet to prevent any scratches during installation. Six friends helped me lift the window through the front of the tank. After a test fit, we moved the window to the back of the tank, and began applying the silicone to the 3.5" seating surface. Because silicone begins to set rather quickly, I had three caulking guns on hand, so three of us could apply 15 tubes in a timely manner.

We applied 1/2" beads all around the surface until it was 100% covered. I realized this would make a mess once the window was set into place, but I figured it was easier to clean excess silicone, than it would be to remove the window and start over if it leaked.

Next we lifted the window into place, and applied uniform pressure until the space between the window and mating surface was approx. 1/4". We quickly put the braces into place while others were removing excess silicone on the outside of the tank. For added protection, I used another 5 tubes to seal around all of the edges of the window inside the tank. After snugging up all of the braces, it was time to wait.