What is the most toxic substance that accumulates in an aquarium?

The most toxic substance that accumulates in aquarium is ammonia

It is highly toxic to fish present in aquarium

This ammonia is produced due to accumulation of fish or plant waste or unused food in aquarium.

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer