Pond Boss Forums POND CONSTRUCTION Selecting a site Pond Design for a beginner

Victor, welcome to the forum.

* If the water is replaced every 10 weeks would I need to worry about algae buildup?
Yes, at least the probability of having algae is greater than not if you don't have any other plants in the pond to utilize any nutrients in the water. It all depends on the amount of nutrients in the water and the water clarity. If the water is clear then yes, the algae will grow even if you bring in new water every week.
* If I make it 8' deep would that prevent it from freezing solid in the winter? Would this could allow me to have fish?
Yes and yes, but unless there is enough O2 for the fish to overwinter, then they might still die even if the water does not freeze all the way to the bottom.
* Would an aerator prevent it from freezing over completely even when the temp is below 0?
Yes and it would keep the fish alive too.

Anywhere sunlight can get to the pond bottom, AND there is enough nutrient nutrients, algae will grow. A 3 foot deep pond will grow more algae than an 8' deep pond if all the other variables are the same.