First, are you using 1.03b? Pop income was bugged in 1.03. Second, who are you playing as? Pops get money from your export income, with large colonial empire you have a lot of pops to share your export money with.
Never set tariffs negative, they are currently not working right and will not give you pops any money. On the other hand, you can set them to 100% and rake in money without harming your pop's income. Also, minimum wages don't give pops any more money.
Pops should only devolve if they have no money and they are being taxed at over 50%. Prior to 1.03b there was also a bug where pops downgraded when parts of them emigrated.
Never set tariffs negative, they are currently not working right and will not give you pops any money. On the other hand, you can set them to 100% and rake in money without harming your pop's income. Also, minimum wages don't give pops any more money.
Pops should only devolve if they have no money and they are being taxed at over 50%. Prior to 1.03b there was also a bug where pops downgraded when parts of them emigrated.