As seen in the picture, there are some bubbles in the middle of the gel. and this usually happens at the left or right side of a gel.
and whenever this happens, I don't use it and throw. it's wasting of both time and solutions.
I'm quite sure that the bubbles are not there when it is liquid state.
this happens only after it becomes hard.
I've already tried several things to fix the problem like washing glasses with detergents or ethanol. but it didn't work. still heppens.
now I'm quite desperate on this.