The way the water element was destroyed was utterly different from the earth element. The yellow energy started from where it entered the body, inflicting damage, and those behind it were moving over it. On the other hand, the element of water was like a river without a bed, going wherever it wanted. Some are smashing its feet while others are scalding its arms.
The poison nature of the water element of the toad wasn't just devastating, and it was rotting Mel's flesh and poisoning him from within. However, the remedy for this was again through the healing nature of the water element, destroying one species while restoring the other.
Although the situation slowed Mel's strength, it was better than dying. The young man survived until the last moment when the healing ability of his blood energy was not enough. He took help from the waters of the pond.