Skunk #1, 15 days old, brown spots

Hi People,

we have recently attempted our first grow, and have already ran into problems. we are only growing 3 plants at the moment, two are at 15 days from seed and one from 8 days.

our oldest and biggest plant is starting to develop tiny yellow/brown spots on its lower two leaves. FYI there is a rather large brown spot on one leaf, but we are aware that this is actually a burn mark from a droplet of water, the other smaller spots seem to be appearing
in a pattern at the tips of each point on the leaf, on both sides. from looking at other pictures this looks a lot like calcium deficiency, but not a clue really.

Here is a bit more info to make diagnosis easier:

How long has this problem been going on? 3-4 days
What STRAIN are you growing? Skunk #1
What was the establishing technique? (seed or clone?) Seed
What is the age of your plants? 15 days old
How long have they been in the soil mixture they are in now? 1 day
How Tall are the plants? Approx 2 inches
What PHASE (seedling, vegetative or flower) are the plants in? Seedling/Vegetative
What Technique are you using? (SOG, SCROG etc) eh?
What size pots are you using? (Include how many subjects to pot) 1 plant per pot
What substrate/medium are you using? What brand of soil mixture are you using?(percentage of perlite, vermiculite...etc?) Miracle grow 75% perlite 25%
What Nutrient's are you using? None
How often are you watering? Bottled Mineral Water every 2-3 days
What size bulb are you using? 250watt envirolite
What is the distance to the plants? Ft and a half
What is the Day/Night Temp? Day 75 – 80 Night 65 - 70
Is the fan blowing directly at plants? aimed at the plants but spins
Is the grow substrate constantly wet or moist? Moist

if you look at the picture called underleaf, there are some small black spots on the underside, but we did repot the other day so it may be soil.

any help appreciated

thanks..

LOL they look fine the spots look like dirt from soil when you repoted dont worry about the small rust spot that may be to do with the eviroment to warm to dry light bit close for such a young plant. dont panic yet wait to see what the new leafs look like if they are normal no need to worry.