You're comparing the ratio of one gas to another in the atmosphere but all those same gasses to water in the tank. Which is apples to oranges, and not helpful because the gas fraction in the tank equalizes with that in the atmosphere.
so what you need to compare is, say, the ratio of CO2 to O2 in the air to CO2 to O2 in the tank if you want to know actual gas concentrations.
this means a ratio, decimal, fraction or percentage. The actual number in ppm tells you nothing about the ratio of gasses.
for example, the atmosphere contains O2:CO2 at a ratio of 21:.03.
This simplifies to an oxygen to co2 ratio of 700:1.
There is sevenhundred times more oxygen than carbon dioxide in the air.
However a freshwater fish tank at 80 degrees F at sea level will contain about 10 mg/l of O2.
This is equal to 10ppm
So if you have 30ppm of CO2 and only 10ppm of O2 you're running an O2:CO2 ratio of 1:3.
1:3 is 2100 times more CO2 than is found in the atmosphere. Your carbon dioxide is 2,100 times higher than the ratio in the air.
and this is why it outgasses. You have to realize that extra carbon dioxide will leak out into the air, but at the same time CO2 from the air can leak into the water, so you'll NEVER have a lower amount of CO2 in your water than in your air. If you did, more CO2 from the air will dissolve in the water and even it back out.
so you can elevate CO2, but as long as gas is exchanging at the surface you can't lower it below atmospheric levels. It will only lose extra CO2, it can't go bellow the 700:1 ratio.
there will always be at least .0145ppm CO2 in the tank. Because that's the concentration found in air.