Hi Malik,
There is no guarantee that if an EA is profitable today, it will be profitable tomorrow. It is determined entirely by the market. As Nicholas has said, and you mentioned too, you should keep all 8 on a demo account, link your demo account to a website like MyFXBook (Check out this video: and monitor the performance, even daily, putting only currently profitable EAs onto your challenge account.
Cheers,
Ilan