You would have to look at the size and length of the joist, and their layout. The size and length of the beam holding them. The size of the posts under that beam and the size of the footing under the posts.
You can post pictures here and we can all make guesses, but this is a call for an engineer.
You have the weight of the water, the tub, and 6 people and what ever the safety factor should be.
We built one house and had the deck started when we informed it would have a tub like that, we over built the deck with double joists, 12" OC bigger beam. After 6 month one footing had sunk 6", easy fix but still not what you want to get into.