Really hard to give meaningful advice without seeing YOUR plants.
But when you say decrease the amount of water during the week, it sounds like they're kept too wet. That can kill roots. Then the plant has not enough roots to support the leaves. If this is what happened, the roots it does have would be nearer the surface, where you may have put too much fertilizer.
All speculation.
If you really want to know what the roots are doing, take one out of the pot and see. Are there well attached healthy roots all the way through the pot Or few roots, and a soggy mess at the bottom?
