If your ina city chances are your water is Ph7 but the only way to tell is by testing it.

Ph is extramly important to solving problems and making you a better grower.

I have had similar results with my seedlings at that stage using proMix. Is that what your growing in? Or peat moss with Perlite?

the last batch of seeds I have started didn't have this problem once I started to add a full On Micronutrient Suppliment. Im not saying this is your problem but its a place to start.. And they should get a little food I mean a little soon....

Once you check you PH first then you can properlly hunt for solutions.

kd