It just bugged me how you described that deck, with 4x4 posts and 4x6 beam, and that professional deck builders would be laughing at our stands. To me it looked like the deck had two 6x6 posts and a 3-2x10 beam, which would pass the international residential code. Somebodies eyes are off. Either mine or yours. Other than the railing, that deck looked fine to me. I hope professionals aren't laughing, whether they are from the North or South. In the southern parts, hurricanes and tornadoes rip apart homes and decking more than the snow does up in the North.
If you were to buy a 300+ gallon monster aquarium directly from a reputable custom aquarium manufacturer, they'll probably fabricate the stand with steel square tubing, which would be stronger than most DIY wood stands or outdoor decks. With DIY it's very wise not to under-build or go with the minimum safety factors since it really doesn't cost much money to make a significant upgrade. Even if your flat broke you can probably find some scrap lumber for free somewhere to make a nice strong stand. Big box retailers skimp on the quality since they have competitive prices, lower profit margins, but deal in greater volumes. Those cheap stands have a very limited warranty and the company which sells them will have corporate lawyers to defend any liability claims. So you won't have much luck suing them when the stand fails. For some of us, it's a given that the stand will deal with uneven floors or moisture problems from either a sump under the tank, a flooded or leaky basement, or if we accidentally overfill the tank. Some of us have kids or pets crawling up or around the tanks also. Some of us may even need to get inside the tank to do some maintenance. So we build extra durable stands which can overcome about anything we can throw at them. It's not a laughing matter when dealing with the possibility of hundreds or thousands of gallons of water on the floor. Monster stands for monster tanks for monster fish should be just as strong or stronger than an ordinary outdoor deck.
