may 7th

Dissolved oxygen comes from two sources. These two sources are from plants and also from the atmosphere. The way the cycle works is during the day the plants produce oxygen so the O2 level is high and then during the night the CO2 level is high because the fish use the oxygen that the plants produced during the day and release back CO2. And since the sun is not out the palnts are unable to turn the CO2 into oxygen.