I just water till it comes out the bottom holes of the cup
Water pours out the bottom right away. Runs down the sides or thru gaps in the dry soil. Next time the pots feel light and you water set each one in a saucer then let them sit in the runoff for 30 min to allow any dry pockets in the soil to become saturated. Then take them out and let them drain or even set them on a shop rag or fluffy towel and to wick any excess water from the pots.
As was mentioned before keep one of those cups full of dry soil so you can feel the weight difference. Hoist your cups when soaked like I said and teh dry one to feel the difference. Do the same thing when you repot to larger ones. By the end of your first grow you'll develop a feel for it and be able to know when it's time without the learning aid any more.
And drop the SuperThrive. I got some and it's bunk as far as I'm concerned.
I switched to a stronger light too. Could this cause the leaves to curl ?
If all was right in their world the stronger light should get them going better. Too strong a light causes the leaves to raise up and the edges of the curl in to try to cool themselves. They can go 'Taco' or here in Canada, 'Canoe'. lol