When in the dark the live plants (including algae) in the tank consume dissolved oxygen and lower its concentration in the water.
(the live plants (including algae) in the tank; consume dissolved; oxygen; T:in the dark) (the live plants (including algae) in the tank; lower; its concentration in the water)
the live plants (including algae) in the tank the live plants (including algae) in the tank
consume dissolved lower
oxygen T:in the dark
its concentration in the water