Could you explain how when someone gives "Sadaqah" his/her wealth will not decrease as the Prophet said in one Hadeeth. Does this mean that one should give wealth all the time? Could you explain this issue with some clarity?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

The saying of the Prophet : "Spending charity does not decrease wealth" is a true statement about which there is no doubt. Its meaning, as Al-Munaawi said is: 'Allaah will bless the wealth of a person who spends (in charity) in this world and compensate it by increasing it, and will additionally reward him/her for it in the Hereafter.' This meaning is stated in the Book of Allaah, as Allaah says: (interpretation of the meaning): {…and nothing do you spend in the least (in His Cause) but He replaces it: for He is the Best of those who grant Sustenance.}[34:39]. Imaam Ibn Katheer,  may Allaah have mercy on him, said: 'No matter to what extent you spend on what Allaah ordered you to spend and made permissible for you, except that Allaah will compensate it for you in this worldly life, and will reward you for it in the Hereafter.' The Prophet confirms the above meaning as he said in a Qudsi narration: "Allaah said: 'O son of Aadam! Spend, I will spend on you." [Al-Bukhari] The Prophet also said: "There is not a day in which the obedient slaves rise in the morning except that two angels descend, and one of them says: 'O Allaah! Compensate the one who spends.' The other angel says: 'O Allaah! Destroy the wealth of the one who is niggardly." [Al-Bukhari and Muslim]

Of course, this does not mean that a person has to give away all of his money. But one has to be as Allaah says: (interpretation of the meaning): {And do not make your hand [as] chained to your neck or extend it completely and [thereby] become blamed and insolvent.}[17:29]. Ibn Katheer said regarding the above verse: 'It means not to be avaricious, and not to be a spendthrift thereupon spending above your ability''. A Muslim has to be moderate in spending, he has to give his wife and family their right and give the poor their right.

Allaah knows best.