Seedlings bending in half

Looks like the seedling is Damping off, and unfortunately, when a seedling has already toppled over from damping off, there is nothing you can do to recover it. The best you can do is quickly remove the affected seedling to prevent the spread of disease to other seedlings. One emergency measure you can try to stop the fungus from spreading is applying hydrogen peroxide. Sprinkle about 1ml (20 drops) of 3% strength peroxide onto the soil of each of your seedlings. The peroxide will kill the fungus. Obviously, there is no guarantee this will save your seedlings, especially if the disease has already progressed quite far.

Spritzing them with a water sprayer will not be enough, you need to get water down deep to the roots.

I see you are using coco from a previous grow cycle. Could be there's some kind of fungus or mold that is attacking your seedlings. Did you use Mycorrhiza and Trichoderma to the substrate? Those can help to get rid of unwanted fungi in the substrate.

Well first thing I see is you are treating coco like soil. It is not soil and does not play by same rules. Ph 5.8 in and out bottom in run off. Coco grows are Hydro in a bag. So it must always be wet, but NOT sitting in run off. I think your ph is not right. Especially if you did not buffer your coco before start. I have grow in coco for a long time. Ph dictates everything in the grow in coco.