Sounds like a unique idea, but I too am afraid of the interaction between the blocks and the chemicals in the water. Like Chlorine, Bromine, Muriatic Acid, and possibly Soda Ash. Of those the ones that coupld cause the most damage are the Chlorine, and the Muriatic Acid. Those chemicals probably caused the damage to the aluminum tops of his water blocks. Along with other possibilities like increased galvanic corrosion, or algea growth anywhere in his loop. Especially since the pool is open to the elements.
I myself would have used a heat exchanger and 2 separate loops. 1 for the systems and one from the pool. That would have allowed for cooling while not worrying about what kind of damage is being done to your water blocks by the pool water. And you still get 95% of the heat dumped directly into the pool. Hmmm.... Too bad I don't own a home or have a pool..... I would probably be willing to give that a shot. Since in the winter it would bring the temps of my cpu well below ambient air temps around here, but still above freezing.
-ouch1