My tomato and cucumber veggie seedlings aren't doing so hot all of the sudden...they seemed pretty happy less than a week ago but are currently deteriorating quickly. The tomato leaves are curling under, paling/yellowing, and almost withering. The cucumbers have yellow streaks and "jagged" edges. Anyone have thoughts or advice about what's going wrong here? Details and photos below.

Timeline: Seedlings are between 4-5 weeks old. Seemed to be growing appropriately up until the last few days

Soil: Each one is planted in Foxfarm Happy Frog, each in a Solo cup (16oz) with multiple drainage holes in the bottom of cup

Temperature: The room they're in fluctuates between 65F-70F. I have a small 6" fan set to low blowing on them for airflow

Light: I have 2, 4' fluorescent lights set up approximately 4" above the seedlings. I picked the lights up used so I don't know the exact lumens but from what I've read it should be enough light?

Pests: I have not seen any sign of pests thus far

Watering: I think I have been watering properly. I water with a slow drip bottle until water comes through the drainage holes. I wait until the top 1/4 of soil is slightly dry and the cup feels lights when picked up before watering again, usually at least 2 days

Hardening off: I've been hardening them off for about a week and a half. I only take them out on good weather days, if it's stormy or windy they don't go out. They are placed in a mostly sunny spot that receives some shade depending on the time of day. I started with 1 hour a day and increased outside time by 1 hour each consecutive day, we're up to about 5 hours a day now. They never seemed negatively impacted by the time outdoors

Fertilizer: I believe this is potentially the issue. I didn't realize that I should have been feeding the plants once their first set of true leaves grew...so up to this point they have been existing solely off of they Happy Frog, which as I understand it is mostly void of nutrients. Today I picked up a bag of Dr Earth tomato/

veggie/herb fertilizer to possibly try a foliar feed...not sure if this is the best route to go or not?