seedlings and watering

[Savag3Kush]

hey, i am new to growing, just got my operation up and running this week. I am growing two plants in pots with miracle grow and 7 plants hydroponically in pots with hydroton. The two plants in pots just broke the surface, but one of the plants has a slight yellowing tip of one of the leaves and seems to be curling under a bit. the light is about a foot and a half up should i raise it more? i water twice a day, and not alot of water, soil seems to be moist at all times! The other question i have is watering schedule. I am using the flood system, but my timer has only 4 settings and i don't have enough money to purchase a recycable timer. i was told to flood 15 min and drain 15 min continuously.Can i just keep the pump on 24/7 and put the air stone in the tray? i was keeping it in the reservoir but it doesn't seem to be doing much, the O2 just bubles to the surface and i don't think is being pumped to the tray where the plants have the benefit of it.

Any advice would be appreciated.