I have worked in the glass buisness for over 10 years and have been building tanks for the past 5 years. The amount that glass can bow is amazing. The 40 breeder is one of my most popular builds, and i use 1/4 inch glas on anything 75 gallons and smaller. A slight amount of bowing shouldnt be a concern. I fyou would feel more comfortable with a center brace, send me a PM and i will send you a glass brace if you pay shipping. The amount of glass that we trash at the glass wholesale company that i work for is more than enough to build most tanks. Let me know if i can help.