urgent help please!

[funtime1]

working on my first hydro grow and everything was going great until yesterday.
I've had my plants vegging for 4-5 weeks.
Two nights ago I switched from 24/0 to 12/12 lighting to put them into flowering.
Yesterday I switched the nutrient solution from the FoxFarm Big Grow to the FoxFarm Tiger bloom. At the same time I noticed a few of the plants were falling over/sagging. I assumed it was because there were getting tall and heavy and their size/weight was over coming the 3" net pots. I was working on a solution to keep them upright and straight when I went in to check on them today and found that every plant one of the two growing tubs was now bent over,sagging, limp, and "wilting". The once very thick and strong main stem is now limp like a wet noodle and won't support the plant and all the branches are the same way - like a wet noodle.
What happened?? Is there anything I can do to try to save them babies? Until yesterday they were doing fantasic!

I have two grow tubs. both have been vegging for the same time and both switched to 12/12 lighting at the same time, and both had the nutrient solution changed yesterday. Only one of the two tubs full of plants is this happening to.

here are some pics of this disaster:

 

[tom__420]

What are the temps?

 

[funtime1]

more pics

as you can see, the plants o the other tub are fine

 

[funtime1]

What are the temps?

not overly hot at all - mid 70's.
In fact, it's been cold and damp weather here the last few days so it's actually a few degrees cooler in the grow room than it's been, but nothing drastic, only a few degrees difference

 

[Green Cross]

more pics

as you can see, the plants o the other tub are fine

Probably stem rot

A silica supplement like rare earth or silica blast can help prevent it, but not much you can do now, but make lots of clones, or at least take cuttings and refrigerate them for a future grow. Check my journal for that process

 

[funtime1]

Probably stem rot

A silica supplement like rare earth or silica blast can help prevent it, but not much you can do now, but make lots of clones, or at least take cuttings and refrigerate them for a future grow. Check my journal for that process

and this would happen over only one or two days and cause this major of a problem?

What do I do in the future to try to avoid this?

 

[Green Cross]

and this would happen over only one or two days and cause this major of a problem?

What do I do in the future to try to avoid this?

Silica supplement strengthens stems, and prevents desease.

Rot can take place in a coupld days.

Have you checked the roots, and the stem where it goes into the medium? Brown roots, smelly, soft mushy stem?

 

[funtime1]

Silica supplement strengthens stems, and prevents desease.

Rot can take place in a coupld days.

Have you checked the roots, and the stem where it goes into the medium? Brown roots, smelly, soft mushy stem?

roots look great, nice and white.
Haven't looked that the lowest part of the stem but around the middle and top it's soft and limp but not mushy.

i'm running out on errands but i'll check the lower part when i get back.

Damn, this sucks! they were doing so well until yesterday