No nutes the first two weeks of life for sprouted seeds, or for cuttings. Then gradually increase at each reservoir change (or weekly) to 1/4, then 1/2, then full strength. A very small amount of B1 such as SuperThrive is good in the beginning, but no nutrients otherwise.

That's too much light to sprout seeds or root cuttings, unless it is way back and covering a bunch of them. For 15 seeds you should have about 18 or 24 watts of fluorescent light, several inches (>5") above them.

Any PH up or down will work fine. Just don't use the real strong acids like battery acid. It's worth it just to buy a gallon of the highly concentrated stuff. Your going to use it eventually.

24 or 18 hours of light is fine for rooting cuttings and starting seeds. After 2 weeks do not use 24 hour light. Plants need their beauty rest too. Here's an argument confirming that: http://boards.cannabis.com/grow-faqs...ut-lights.html

15 plants in a 25 gallon reservoir sounds fine, depending on what you are doing. Right now I've got 11 plants going in 3 gallons.

I hope that helps a little.