Is there any part in Qalqala in which whenever we see a halqi letter and after it is Qutub Jadd (qalqala letter) then we do not apply Qalqala?

Question
Assalamualaikum wa rahmatullah wa barakaatuh

I have a question regarding Tajweed.
Is there any part in Qalqala in which whenever we see a halqi letter and after it is Qutub Jadd (qalqala letter) then we do not apply Qalqala?
Also, in Surah A'raf we see around ayah 50's or so.. the word Basta tan..on the sawd there is a seen..what does that mean and which rule is it?

Answer
Wa alaikum assalaam wa rahmatullah wa barakaatuh.
If the letter in the group is not saakin (meaning has a vowel) then it will not have a qalqalah on it.  For example if we are reading and continuing (not stopping) on the word there would be no qalqalah.  If we stopped on this word however, there would be a qalqalah on the second because now there would be a temporary sukoon on it. 

In the word: the word is written with a , but Hafs 'an 'Aasim by the way of Ash-Shaatibiyyah pronounces it with a .  This is the small is written over the .