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We decided to use SeaView on our tank's backdrop finally, and I must say that I'm pleased with the results!

The stuff is kind of messy...like baby oil but more thick and sticky.
You rub it all over the backdrop and then press it to the back of the tank to create a seal. The hard part is getting all of the air pockets out, but a ruler can help.

Photos don't show the difference too well, but here's a before and after comparison:

I'm not sure what this does, it makes the background more vivid?

Yes it does.
Their web site is http://www.seaviewinfo.com
Check out the video demo of it.
I got a tube at Petco for around $5.

It also makes the background "seal" to the aquarium, right? I was thinking about trying this stuff myself. I've used the watercolors background that you put on with soapy water, squeegee out the air and it's the next best thing to paint. I'm hoping the sea view is similar.

It works the same way.
I still had to use a bit of tape to secure the edges, but the rest sticks to the tank just fine.