If you are reading any dua to being your fast then what you are doing is a bidah.There is NO dua which is to be said when you start the fast. Only the intention (niyah) is required which is NOT be said from the mouth but ONLY from your mind (niyat).
Prophet (peace and blessings of Allaah be upon him) said: “Actions are but by intentions, and everyone shall have but that which he intended…”(Narrated by al-Bukhaari, 1; Muslim, 1907)
“Whoever does not intend to fast before dawn, there is no fast for him.”
(Narrated by al-Tirmidhi, 730)
The intention (niyyah) is an action of the heart. The Muslim should resolve in his heart that he is going to fast tomorrow. It is not prescribed for him to utter it out loud and say, “I intend to fast” or “I will fast tomorrow” or other phrases that have been innovated by some people. The correct intention is when a person resolves in his heart that he is going to fast tomorrow. read more :Uttering the intention to fast out loud is an innovation(bidah)
Authentic & UnAuthentic Dua for Iftaar !!!
Invocations for Breaking the Fast
176. Thahabadh–dhama u wabtallatil-urooqu, wa thabatal-ajru inshaa Allaah.
The thirst is gone, the veins are moistened and the reward is confirmed, if Allah wills.
Abu Dawud 2/306 and others. See also Al- Albani, Sahihul-Jami’ As-Saghir 4/209.
177. Allaahumma innee as aluka birahmatikal-latee wasi at kulla shay in an taghfira lee.
O Allah, I ask You by Your mercy, which encompasses all things, that You forgive me.
Ibn Majah 1/557 from a supplication of Abdullah bin ‘Amr. Al-Hafidh graded it as good in his checking of An-Nawawi’s Kitabul-‘Athkdr. See Sharhul- Athkar 4/342.