I didn't say it was a HARD problem.
If you feel I have insulted your intelligence try this one:

If you have 5000gallons of water(closed system) in an ammonia equilibrium with a pH of 10 and 20ppm H2 as an Oxygen scavenger,
How many litres of air must be added to lower pH to 9?

Winner gets $1.20 on Stars!

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