I don’t think there is a specific amount to be used for gambling, or a certain percentage of your income for gambling but it always advised that you gamble with what you can afford to lose. If you can afford to lose 5% of your income then that the amount that is advisable for you to gamble with. We have all seen people who don’t discipline about gambling and we end up seeing them losing so much in gambling and we this you can easily turn to an addict.
That's were your hole problems lies as a gambler because it seems you don't have a specific direction or target while gambling. In gambling once you can't figure out your limit or boundaries you become a slave to it.
Many people today become addicted to gambling because they keep chasing their lost recklessly without knowing the implications and how harmful it could be. However any gambler that doesn't no when to call it a day, and allows emotions to be cloud is sense of reasoning, is actually not been fair to his own self because the aftereffects can be too disastrous on him.