Is this a burn from the light?

I have 3 plants, 2 hawaiian snow (the tall ones with narrow leaves) and one early durban. The edges of the leaves are crisping and turning yellow. At first it was only happening to one plant, and now it seems to be happening to all of them. I just moved them to about 20" away from the light, they were about 12" before. They're 5 weeks old. I'm using 20-20-20 nutes. Is that a problem? Someone told me that would work fine. I water thoroughly once a week, feed every two weeks. They're in 2.5 gallon pots. The temp is 81.5, it goes down a few degrees at night. (maybe 3-5).
Any help would be appreciated.

81 degrees? I think thats a little too high temp. for the plant, you should try to get it down to 75 somehow i think that's an ideal temperature for them. just my two pennies.

It looks like it could be a burn from the nutes. How much do u give when you do feed them? the only other thing i can think of is bugs but it doesnt look like thats the case.

moving the light would havel helped looks like you burnt them to me

81 is way to high get some more ventilation in there m8

definatley bulb burn the bulbs are toching the leaves, this happend to me on my first grow constant problem with CFL lights.

Also, looking at that gap around the edge of the pot, that droopy plant looks thirsty. Give it a good watering, and it should perk back up.

I don't give them much nutes at all. I only put just under 1 tsp per gallon, and this happened when I hadn't given them any for a while. The light is pretty far, it's not touching the leaves. Would a fan blowing directly on them be a problem? I'm gonna try lowering the temp and see if that helps

I had something similar to this. It was a combination of heat wind and light. The room was too hot and the plant was kinda sweating in a couple areas and leaves were touching other leaves, almost clumped together. I had a fan blowing kinda at a downward angle which was blowing the leaves together that were sweating. I changed the fan so it was sitting lower and blowing up towards the light and added some ventilation to cool the room. A day or so later the leaves were white like that and kinda shriveled in places and crisp but it survived. I hope this helps and good luck.