You'll be happy to know that no algae has ever grown on the Lexan surface of my MacQuarium yet and I've had it for several years now. Currently I have a very content Betta fish in there for about a year now and he is quite active considering that most Bettas I've seen just sit there. As for the cat in the harness, it wasnt my cat (just visiting) but, for the record, the owner claimed the cat liked to go for walks on the leash :)
http://vividpicture.com/aleks/macquarium/