Strange Gray-ish splotching, then yellowing, then curling and twisting

Seedling about 2-3 weeks old under daylight CFL, FFOF soil, seed is pineapple express from G13 labs about 1 year old. Using only RO water so far, no added nutes. I popped this into FFOF without knowing that can sometimes burn them, but no sign of nute burn. Plant was doing OK but as you can see the 2 oldest lowest leaves are deteriorating. Started with the gray-ish, color is like the lead of a pencil, splotchy areas in middle of leaves, between the veins. Then those lower leaves started to yellow and curl.

I don't think it's nutrient burn since it has done well so far. However, I did turn down the heat in the room and it definitely sat at mid 60's F for a week or so. I just turned heater back up to keep it at 75F last night. Also, the new leaves seem to be ever-so-slightly less green than before.

Do you think this is temperature-related nitrogen lockout in the mid-60s F? I thought seedlings this size/age required very little nutes and FFOF would still be more than adequate at this stage. Watering every 4 days or so, testing soil moisture with fingertips down an inch or so.

Also, there are small "gnats" on the soil - they don't seem to ever be on the plant itself, and stem is still hairy and I see no signs of them eating it.

I'm thinking about just chilling with the temperature correction for a while first, then adding small dose of nutes if that doesn't help, but looking for any suggestions.

2 much water

Interesting. I guess compounding the issue is that I decided not to "graduate" pot sizes, but rather put the freshly germinated seedling in a big 3 gallon pot. Didn't want to put it through the shock of transplants. For all I know the bottom of the pot might be wet as heck while the top seems bone dry.

Now I am very concerned those gnats may indeed be fungus gnats.

For now I will back off the watering and keep everything at 75F and see what happens in the next few days...

yep........ probably be almost two weeks before you need to water....... I dunno for sure but something like that......... when your soil dries up the gnats will go away........

Thanks man! I will try this and see what happens...

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