White Widow is a pretty hardy strain it clones well. 5 inches should be able to take light nutes. Strange. You can veg under a HPS but get another MH when you can. Light not too close ? The big question is your medium and did you gently wash off all the peat pot ? If the peat was not washed off it will be all in your system, cloged lines and worse. TOO wet at the rootball, I think damping off it's called. The roots that hang down can stay in water all the time but not the rootball it like air. One more thing, Do you have calmag+ to add back to the water. That can be a lack of magnesium. Cause nute lockout. And how's your PH, it can cause problems and lockout too ? Pictures help, if you can you will get much more help. A pic is worth a thousand words.