Hybrid poplars have large, aggressive, shallow root systems that will search out water to sustain the vigorous growth of the tree. How far is the tree from the house foundation? Roots will typically redirect when they hit something solid, but if they find a flaw they will readily grow into it. You would probably need to consult a structural engineer to determine whether flashing would be an adequate solution. The tree certainly could press through it, but the roots are more likely to follow it. Again, a structural engineer would make that call.

Your poplar is likely to make it to 50 years, and perhaps several decades more. The dwarf pear tree roots will not extend 25' to the pool. You can prune the poplar roots by trenching, but that will need to be repeated annually for best effect. Physical barriers may also be used, but they would likely need to be more substantial than aluminum flashing. Tree root barriers are commercially available, but even when installed to a depth of 3', the roots will eventually find their way under.

Thank you for the quick response. The tree is also approximately 30feet from the corner of the house and like I said a 3 inch root is 10 feet away. Also do you have a list structural engineers in the Big Rapids area. 
Rick

I unfortunately don't have a list of structural engineers, and I don't see a simple way to find someone through the state's website. You can lookup an individual to see if their license is current, but not search by location.

I would feel more comfortable with your poplar if it were at least twice that distance from your house foundation, but 30 feet should be manageable if you want to keep the tree. The other thing to think about is your drain lines, both your main drain to sanitary sewer and any storm sewer, including the drains around your footings and any lines moving water away from your house. The poplar roots will aggressively invade through any cracks in those drains, and that can quickly become a very expensive problem.