Accounts with small budgets (~$500) can be extremely difficult to optimize because there’s often not enough data to recognize patterns.
For example, if a keyword got 1 click last month and 1 click this month, should we increase the bid for that keyword? Well, 1 click is not enough information to make an educated guess.
In this case you may need to manually edit the budget twice per month because you want to spend the majority of it in a short amount of days and then pull back.
Do not turn on monthly budget because then it will spend that money evenly throughout the month, which isn’t ideal.