i have heard that the salts in tap water will do that if can collect rain water or if out in country look for small stream or spring or river because they are fed by springs, rain or melting snow or ice just check water ppm before useing it to make sure if plants and fish live in it ilbe safe...
the soil you are useing should have a very low amount of nutes in it could be soil is to potaine or light to hot for seedlngs or dry out the seedlingnrrds a moister tent for a week becuse it should be ok if it sprouted if the seed was to old it would not have sprouted hope this helps
i think you need a fan to make your plant strong and for air movment if you go with hps you will need more fans but would help with cold house cfl proably whould warm a small closet ok with enough light to for good grow autos proably good idea for small space but not sure of the amount you want
realy use closet or a grow tent search on line there not that expencive because if you do and grows great the coloms wll be close to the size of you pc case
get a 3 gal plant contaner with holes in bottom with under nith tray , good garden potting mix not soil but mix. germante seed for first time something like nothern light strain put gemanated seed in potting mix ,water thoughly put light close to contaner not to hot and not to cold room temp...
looks like the leaf below and above are getting it to me also it mite be the start of cal .defencey what soil are you using and are you feeding nutes and possably got a nutes lock out
you what you ppm as low as you can to start with use rain water if can its free if not buy water or a ro of some kind to lower ppm just add more downer but may go back up after 24 hours thats what to me so i started collecting and ueing rain water and spring water with little ppm and stoped...