Leaf edges curling under.

The plant is four weeks old on its 5th set of leaves and has undergone a transplant recently. The problem is isolated to the fourth set of leaves where the edges curl dramatically under. The curl starts at the base and covers about 75% of the leaf leaving the tip intact. The entire plant is a healthy shade of green with no discoloration or spotting.

Specs:
1. Transplant went from a half gallon grow bag to a 5 gallon container filled with neutral topsoil, perlite and Foxfarm's organic potting soil.
2. Lights - 2 cfls: Cool White and Warm White. Kept 2 inches from the top.
3. Nutes: GH's Flora - Vegetative growth stage ratios.

The only thing I skimped on during the whole grow process occurred during transplant where I didn't have massive amounts of RO water available and had to use icky tap water. Sorry 'bout the lack of pictures. I'm curious to see if anyone can identify the problem off the top of their head.

 

The plant is 4 weeks old since it emerged and yes there are 5 full leaves and sets 6 and 7 are maturing as we speak. The upper growth has slowed but the new growth at the nodes are filling the plant out really fast.

Ferts just started at week 3 because I wanted to hold off until I knew the plant was butch enough to handle it. As for air, there's an oscillating fan that I turn off and on throughout the day. There aren't any visible insects, crawling or flying, that I see other than an ocassional earwig and small beatle; they usually are KOS once I catch 'em and are made sure that they endure a slow and painful death. I checked under the individual leaves and they don't seem to have anything unusual underneath. The tops of the leaves still don't have any black or white spots, or yellow that would indicate a bug invasion.

The curling seems to be spreading to the newest growth and I'm guessing will spread throughout the whole plant. Oh and thanks for helping 420

 

The plant was watered once when transplanted from a small plastic cup to the half-gallon grow bag. The soil didn't require any waterings for 2.5 weeks. It was then where it received its first dose of the GH nutes at the recommended vegging values. A few days later was when it was transplanted from the half-gallon to 5-gallon container. I probably should have tranplanted her when I watered after 2.5 weeks which is where I think the problem started.

The leaves seem to have improved in the past hour where the leaf is only 50% curled under as opposed to 75%. I think the 25% of that curl loss was transferred to the upper growth and is slowly dissipating upwards. I guess my problem was overwatering during that time where I watered at 3.5 weeks then at 4 weeks (with horrible tap water to compound the problems). When I watered during the last transplant, I only used SuperThrive and no nutes to prevent burning if there was heavy root damage. Seeing as how I gave the plant nutes a few days prior, there was no point anyway. After the transplant, I foliar sprayed a solution of a very fine amount of nutes and epsom salt. Hopefully the plant perks back up in the next couple of days. So do you think it was the combination of overwatering and pH imbalance, or leaning more towards overwatering, or is there something else I should be worrying about?

Oh and about the size of the plant: isn't it normal for a plant to gain about 1.25 sets of leaves per week without nutes? I don't like comparing my plant to other people's plants but it seems to be on par with the average plant. I'm not sure about that though. Thanks again for the help and the really quick reply.