Answer:
1_11/20 pounds, or 1.55 pounds.
Explanation:
Since at the beginning, he had 5 1/4 pounds and used 3/5, we subtract the amount of pounds. We are then left with 93/20 pounds, which he then splits among 3 containers. Dividing by three, we then get 31/20 pounds in one aquarium, or 1 11/20 pounds in each aquarium or 1.55 pounds.