The total available ClO2 from a 28% solution is quite high.
The activation is not totally efficient, so there are some losses. A 28% solution of sodium chlorite should be capable of producing 280000 PPM of ClO2. However, because of the inefficiencies, only about 60% of that is actually produced.
That works out to 168000 PPM ClO2.
We further have to reduce this because the 28% is not totally pure. It is only about 80% pure, so our 168000 is reduced to 134400 PPM.
If we look at 1 drop of the 28% sodium chlorite solution, and fully activate it by using a very low PH acid, it would produce about 8 PPM free ClO2 in 1 liter of water. If we were shooting for a 1 PPM free ClO2 solution, we would need about 8 liters of water.