Correct watering procedure is to add enough water so that it comes out the bottom drainage hole. If you only ever water by pouring a small amount on top, two things happen.
- Since the water is always all up at the surface, root systems remain shallow, and don’t grow deeper in pursuit of water. Deep roots is what gives a plant reserves for a drought event, such as when you forget to water. If the roots are all up in the top layer of soil, then when that top layer dries out completely, they’re toast.
- Watering flushes out accumulated fertilizer and mineral salts from the soil. If you always add the same small amount of water, it carries these salts down to the same level in the soil every time, and eventually you end up with a layer of salts. In a terracotta pot these will come out through the pot wall, appearing as a layer of crusty salts on the outside. You can also get salts on the surface of the soil.
So what you’re currently doing for watering–adding only a small amount on top that isn’t enough to flush an 8″ pot–probably isn’t overwatering. What is happening is that the seedlings’ roots are shallow, since “on top” is where the water is, so when the top layer of soil is dry, that’s a drought event, and out of a potful of seedlings, one of them is handling it worse than the others, which is how natural selection works.
An 8″ pot is too large to start basil seeds in. The excess unused wet soil with no roots in it can go anaerobic as the water carries soil particles downwards and compacts them, removing air spaces between them. Next time, use something like an ordinary 2″ to 4″ pot, and figure on thinning and transplanting.
I’ve been looking at your plant diary. In your situation, you need as much light as possible on these, so I’d bring back the reflector. Mylar or white works better than aluminum foil. http://www.growweedeasy.com/reflectivity
Honestly, you’re wasting too much time on trying to do the math to calculate whether your plants are getting enough light. Don’t do math–just observe your plants. As they grow, they’ll tell you.
CFLs are fine, but you can load them up without having to worry about scorching and too much light. It’s the people using high-output marijuana grow lights like metal halides and multiple arrays like a 4-tube T5 or T8 that have to worry about scorching. If you’re working with ordinary table lamp bulbs like CFLs and LEDs, it’s not usually an issue unless you get, like, dozens of them all lined up.
If you have a tiny seedling so close to a CFL or other fluorescent that the leaves are actually touching the tubes, it can scorch, but otherwise you want the leaves to be 2″ (yes, two inches) from the light. Get a ruler and measure it. It’s right up under there, yes.
A two-tube T5 fixture is so much easier to work with than a flock of single CFLs in household lamps, it expands your options quite a bit, and it doesn’t take up that much of a footprint on the table or shelf.
I’d look for 100 watt equivalent on the CFLs if your light fixture can handle it, and I’d also look at 100w equivalent LED household bulbs. They tend to be on the heavy side in something like an architect lamp, but you can move the pot to where the bulb can shine on it.
Plants can be grown under lights 24/7, but most people shut off the lights at night for human reasons. If basil starts to flower too early, just pinch off the flower buds. You’re not growing weed here, where you need to manipulate the day-length in order to manage a flowering sequence.
You thinned your basil too early. Generally you wait until they all have at least two sets of true leaves. This gives you a much better handle on which ones are the strongest keepers.
I don’t see it mentioned, but if you don’t have one yet, get a cheap lamp timer to run the lights, it’s so much easier than having to remember when to shut them off.
Also, don’t move them around from window to window. Every time the lighting changes, the plant has to adjust its leaves, which wastes energy that it could be spending on growth. Pick a spot and leave it there.
Was your Miracle Gro potting soil that kind that says “feeds for 3 months” on the label, or says that it includes MG plant food?