LOL! Over-watering in a DWC... HAHAHAHAH! Sure...
The problem you're experiencing is a magnesium deficiency. There are many ways to get a magnesium deficiency, so let us cover the bases.
Firstly we have pH. Low pH (especially the kind found in hydroponics) can have a negative effect on magnesium uptake. You need to make sure you keep your pH stable at 5.5. If it goes anywhere, up is a good direction. Below 5.5 and you get this kind of problem on some strains.
Next there are nutrient toxicities. Excess Calcium or Potassium are going to compete with Magnesium for uptake. Sulfates can make it worse, so Epsom salts are not always the answer. More nutrients might make the issue worse, and fresh water flushings will only leach more nutrients from the plant. After checking the pH you should then check your water hardness level. If the water isn't hard cut your Calcium supplement (if any). If the problem continues into new growth, or if you see calcium deficiency, then your issue is probably potassium. Maintain a balance with your nutrients through out the process, never excluding anything but trying to find the culprit all the same.
The reason you are seeing Nitrogen-esque issues has to do with nitrate mobility with magnesium. The two generally show up together, but nitrogen shortages are uncommon with nearly all nutrient systems so long as your ppm levels are correct and you're following closely to some kind of schedule.
I find many Skunk related genetics require a little extra Magnesium during week 3 to 4 of growth. Then again during the first two weeks of flowering, and again in weeks 4 and 5. I'm learning that Magnesium is in high demand during certain times with certain strains and maintaining the balance of pH and other positive elements (Ca+2, K+1) in your solution. Without the magnesium you need you'll see interveinal chlorisis, the yellowing and eventually necrosis of the "meat" of the leaves. This is because Magnesium is the most crucial element to chlorophyll and the production of energy. Without it the chlorophyll burns up and dies out. Hard water associated deficiency is usually accompanied by a potassium deficiency (curling of the ends of leaves). I didn't see that, which is why I'm leaning towards pH fluctuation. High temperatures and high humidity can reduce transpiration rates as well, allowing the immobile element Calcium to build up while other more mobile elements are consumed.
Still, I think the problem is pH related. If it isn't, then Calcium. Then Potassium.
A solution to your issue would be to use a product like Organicare Huvega as a foliar spray. Applying the magnesium from this organic source directly to the leaves can quicken the recovery and reduce the long term damage to the leaves that have suffered.
Expect the problem to get a little worse even if you fix it immediately. These things take time. Concentrate on keeping new growth healthy and dialing it in with the nutrients. If the problem is "genetic" you'll see it clear up without changing anything at all. But be ready to pound with with magnesium in flowering.
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