Peculiar Problem????

Parts of the main stem and some of the other side branches have developed a strange dark mark on them. looking closer, the mark appears to have made the stem become flat in the dark area. it is smooth to the touch and even a bit waxy. One side branch which has the problem has bent over slightly, and i have noticed that a lot of the plants stems feel quite soft and bendy.
What is the nutrient i need to introduce more of to get a stronger stem?
thanks for any answears.

Tell a little more about your plant. What stage is it in? How old is it? Where do you keep it?

It has been flowering for 5 days, it has already got pistils coming out everywhere, its about a foot tall, perfect formation, very healthy and green, greenhouse ams strain. except these marks on the stems that are smooth and that dont any of the little hairs you get on the stem, the plant is fine. the marks arent that big at all but they dont llok normal

It's almost impossibe to tell without a pic. Could be a lot of things...it sounds lik "damping-off" go to google and search that term then look it up in their pics. See if it is anything like that.

to help those stems, you must first help the roots. I would get some humic acid and mycorrizae fungi. Humic acid keeps the roots clean while the fungi pumps them up, i did this with my plants and my stem are rock hard and thick.