Once your population drops below 80% of your max population, your production begins to drop.
The lower you are below 80% the greater the penalty. To recover to 100% production the *fastest*, sell as much of your RES tech, set tax rate to 0%.
Once you reach 80% of your max population switch your tax rate to max. (because at this point, the increase in population no longer benefits you). Whereas raising your tax rate lowers your max population.
Max Population Formula:
(1-0.95*Taxrate)*(24*Res+12*Land)*ResTech*GvtPOP*BioFactor
Population Growth Formula
Min(BioFactor*Trunc(Round((MaxPop-CurrentPop),0)/3,0),BioFactor*Max(40,Round(0.03*(1-Taxrate)*CurrentPop),0))
References:
http://wiki.earthempires.com/...lation#Maximum_Population