From the information provided, we can say that he is not correct. This is because the depth of the water is the only measurement that he is using to make his estimate. Comparing the depth of the aquarium and the bucket is one measurement, but both the aquarium and bucket are most likely of different shapes and sizes. Therefore, this equates to more buckets for the same amount of depth in the aquarium. To get a proper estimate on how long it will take he needs to calculate the volume of water in the bucket and compare it to the volume of water needed to fill the aquarium.
