I actually did a lot of research before I got it. I bought it straight from the breeder and he answered all my questions as well.
And what did the breeder state about size of tank, temperature, pH values, etc? Do you know the actual species, or did the breeder just refer to it as a "white sturgeon"? You are asking for help about a fish when no one here even knows for sure what you have? Let's start with the species of sturgeon, not a common name.
That aside, personally I think that keeping any sturgeon in a 29 gallon tank during a heat wave is just asking for trouble, as that small of a tank is going to get warmer, a lot quicker, and overall be a lot more unstable than a larger tank. Sorry, but this isn't sounding to me like you did a lot of research.
Use ice cubes, frozen pop bottles filled with water, run fans across the surface of the water, insulate the tank, do cool water changes, etc. 74F is still too warm.
Perhaps you should discuss some of this with the breeder.