Original Student Sentence:
Aquarium visitors saw a dramatic increase to reach a peak at appro 35% in 1985
*confusing: "to reach a peak at appro 35%"?
In 1985, the aquarium's attendance increased by approximately 35% (compared to when?)
The aquarium's attendance reached a peak of approximately 35% in 1985.
And many more options...
Consider placing your subject at the beginning of the sentence.