...if you're keeping 'em in dirt (or a dirt-like substance), then an ingoing Ph of 6 to 6.2 or 6.3 is fine.

If you're doing any kinda hydro, 5.7 is what to shoot for, tho 5.5 to 6 will be fine.

If you can check your runoff, ideally, it, too, should be what is going in. That means that the general Ph of your medium is what makes the plant most happy, and most nute-uptake-y.

And YEAH, git mo' light on dem bee-yotches! Just make sure the temp doesn't rise above 28-29c max, and a 'night' temp of 17-23c.

As far as Ph Down goes, while in seedlingland, maybe you can get away with the lemon juice or vinegar for a bit, but get yourself the smallest, most inexpensive bottle of 85% Phosphoric Acid as a Ph Down, and try not to use a Ph up unless your natural water calls for it. Some say that the use of vinegar promotes the wrong type of soil beasties, but the jury is still out on that one.

Do NOT use Baking Soda as a Ph 'up'. Old school advice.

Also, use either R/O or Distilled water at first, working up to carbon filtered water if you need it, or R/O all the way if it's not too expensive. Not necessary if your base PPM of tapwater is less than 200 or 300, iirc.

More Lumens are Not a Bad Thing (tm).