Weak stems

it's too much branching and competition between branches for light. Genetics plays a role too - some can handle more branching than others. This is mostly an outcome of your choices several weeks ago. you only need 2.5-3 colas per sq ft to maximize yield per sq ft. More only makes for situations like this - a floppy plant with excess branching and tiny buds spread out all over the place. Get some garden wire and start getting things vertical again. You don't want stuff hanging downward. Apical dominance is still important and anything drpoping will get resources than if they were standing up properly. Use a scrog for support in future just in case you run into some weak genetics in regard to stem strength. grow fewer colas per sq ft to avoid it with plants that aren't prone to it.

I agree with the answers provided below. Other forms of Si are rice hulls, Wollastonite mineral additive for soils. or a acid from of Si, its very expensive though. Some other forms exist like Potassium silicate but their PH is crazy high "alkaline" and when it lowers it can get locked out and react with other items in the mix then fall out of solution.

I addition to what Krisis said… In the future try incorporating some silica in your grow. Silica helps strengthen stems and makes em nice n strong to support the weight. I use diatomaceous earth for my silica.

Lots of plants will need to be supported once buds start putting weight on. This is why many people use stakes, trellis, or tie branches up. Some plants can support on their own and some can’t