I have been instructed to design and construct a outdoor pond! I have a wide experience in aquariums but never had anything to do with a pond before and especially not build one so this is going to be really interesting! I will get access to everything I need, for example people who carry out the practicality of the construction, and the budget is high, so I have high hopes to be able to fix it up real good! The idea is so low-tech as absolutely possible! That is so natural filtration as possible. Has only planed to use pumps that carry around the water for the filtration depending on what that will be, but more on that later! I dont have they exact dimensions, but approximately 25meters 10-20m wide and 10m deep at its deepest point. 33feet to 66feets wide and 33feets deep on its deepest spot. So with zero pond experience, I feel I have a lot to learn and need some help! What is the best to fill the bottom with to keep it sealed? What do you think about the filtration of the pond?