I just turned my city of 65k with $7m into a city of <5k pop and -$700k
Thats what happens when developers create moronic requirements to unlock specific monuments!

Lost about 2hr of progress, and another 1h-90min trying to recover it.
I had absolutely everything switched off, but the cost of roads and stuff like that was dragging me under, and neither 1% or 29% tax or anything in between would help me balance the books.
The ones that killed it were 50% crime for 5 weeks. I got it there for about 2-3wk by turning off the police, however that only did about 25%, i needed to upset people to push them to crime, so straight to 29% tax (it came right after the monument for having '-1' balance) which helped put money back in, but the high tax sent people flocking the city and in doing so all the criminals must have left cos the crime rate dropped.
As soon as the population plummeted there was nobody left to tax, and despite switching a load of stuff off, it never seemed to balance
-1 credits, 50% crime, and 1000 abandoned buildings for 5wk... attempting all of those at once... not a good idea.