Answer: There are several possible causes for this. One is that they are being attacked by insects. Examine the plants very carefully under a bright light, checking the undersides of the leaves and along the stem for signs of insects or webs or any thing else out of the ordinary.
Another possible cause is overwatering or underwatering. Most houseplants prefer a soil that is evenly moist but not sopping wet. To see if they need water, check the soil with your finger. Also, when you fertilize, be sure to follow the instructions on the label because over fertilizing can damage plants.
Finally, although you have them under lights, it is possible that they need even more light. If this is the case you will notice that they are growing taller and "reaching" for the available light, possibly even leaning oddly as they stretch for it. If this is the case you may need to add more light either from lightbulbs or a sunny window.
Good luck with your plants!
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