Why are my seedlings getting thinner

[guerrillauk]

My young seedlings, still developing their second main leaves, are slowly getting thinner towards the middle of thier stems, however this is only happening to two, out of my 8 plants, the others are perfectly healthy, any advice to help the plants? Or to stop this happening to more? Please help!

 

[CO Finest]

Are they reg or fem seeds?
what kind of lights and how far from seedlings?

 

[guerrillauk]

They're a mix, however my autos seem to be the ones doing better, they were placed on a south facing windowsill, watered once a day with just enough to keep then moist for the day. However since seeing this I've ordered a 125w duel spectrum cfl, just to keep them going before I decide thier strong enough to go outside

 

[brightlight]

This is symptomatic of a condition called "damping off." It is often caused by too much moisture or humidity.

 

[labexperiment]

Water her until you see water come out the bottom of the pot, then do NOT water daily, wait till the soil is mostly dry before watering again.

 

[brightlight]

Labexperiment's watering advice is sound, but I'd completely eliminate water on the impacted plants until they become fairly dry because damping off is caused by pathogens that somehow affect plant when too much moisture. More water again may do it in. Sorry to say but seedlings that get this are pretty hard to save or get back to normal.