Hey hey, ho ho, hows it going. I'm not skilled at problem diagnosis, so when I get a problem I always refer to the problem charts. I posted at least three of them and I know there are many more (maybe search "problem chart"). Somewhere in this forum is even a couple step by step, flow chart-type diagnosis thingees, ie. If the problem is only on the lower leaves, go to step 6.

You say your pots are pretty wet, and you are having a problem with algae. Sounds like overwatering, or lack of ventilation. Both are a common noob mistake. (Nothing against noobs, it's impossible to become experienced without first being a newbie.) Like GL asked, what's the temp and humidity? Optimum is 82 and 60 respectively at the canopy. You should only be watering after the soil has dried out. On some of my plants this is nearly 2 weeks. Not only should you be venting your lights, but it is very important to vent the grow area as well. Not only will it help keep down mold, moss, algae, etc. but if your plants gently rustle in a breeze they will grow bigger, and be stronger so they can support the weight of the huge buds they're going to have.

What's a vegging box?

I wouldn't worry too much about purple or pink stems at this point. Though it can be an indication of a nutrient surplus/deficiency, your plants aren't looking real bad at this point and I wouldn't be real concerned. Some plants just have purple stems no matter how healthy they are.

Be sure to read up on how to vent well so you don't have to tear apart your grow 3 times like I did. Can't tell for sure from the photos, but it looks like those fluorescents could be a little closer to the plants. That's one main advantage of fluorescents and it makes a big difference if they are close.