If there are stairs there and the joists are on trimmers to meet the stairs that weakens things. But you're losing/confusing me about the layout now. Hard for me to say.
Either way, if you want a 300, you want to know for sure whether it'll work. I don't say this as a salesman for my own 300, but just in general. The difference between mine and an acrylic is 300-500lbs, but that spread over 5 joists is not that big a deal... it's the water weight that will make the big difference. If you're on open web trusses on 16" spacing you should be OK unless it's parallel to the stairs. But it's worth knowing for sure.