6.7 water pH is a bit too high for soilless, bring down to 6... 6.5-6.7 is ideal for soil, but soiless is lower.

If water is too hard it could be a problem.

Light is too low, they can't use so much light until they are healthy. Even then, a palms distance is very close to a 400 mh. Having the light so low right now is causing additional stress. I'd give them a couple feet at this point.

If there isn't enough air circulation it'll make things even worse, make sure you can see the leaves moving in the breeze.

They also probably won't need more food until they are healthy. They are really small for 5 weeks, so they haven't been using much nutes, but if you keep adding they will build up. It can't hurt to do a soil test and see where your pH is at, as well as if NPK is too far off...