looks like heat and sunburn damage.

I am using fluorescent lights which generate very little heat

Assuming there is no sign of pests then I'd bet on the fair amount of leaf edema showing there - the puckering/lumpy bumps in the leaves. A watering issue. Tissue cells in the swollen puffy areas rupture and die and the patch falls out of the leaf. Clue is that it is usually internal leaf tissue that deforms from the edema, not the leaf edges and you see brown tissue edges around the hole.

Dave

I once saw similar damage on my cuke seedlings and realized that when I took them outside on a nice day that a slug had crawled into their planting tray. If you don't see a tiny caterpillar hidden in the leafs/stems (another possibility) I'd check the under sides of the containers for a rogue slug.

Hat tip to Dave. That's edema, and edema is often caused by drowned roots. The plant tries to take up water faster than it can transpire, and the leaves blister. Increasing illumination can help, as it helps the plants disgorge the extra water. Same with extra ventilation, and lowering humidity. That being said, magnesium and calcium deficiencies can make plants more prone to edema.

I only water once a week though...is that too much?