Don't use the labels on the bottle. They are completely worthless...
This is your feeding schedule...
http://generalhydroponics.com/site/gh/docs/feeding_sched/GH-FloraSeries-REC-Charts.pdf
You want to start your plants @ REALLY low dosages. @ 3 weeks I would be aiming for 200-250ppm. You would be surprised how little a small marijuana plant needs.
My suggestion(s) - Flush the reservoir and scrub it real good with a 30:1 bleach solution and rinse well (obviously). Pick up a product called AquaShield from Botanicare, it'll help keep your reservoir from slimey. I've tried many things (including h2o2) and AquaShield has been the most effective.
Because you are using distilled water, you will need to add Cal Mag Plus (or equivalent) as well. Nutrient MFG's leave these out because tap water usually contains more than enough of them, but if you used distilled you don't get any.
Mix the reservoir following the proportions on the feeding schedule, not the bottle, mix to 250ppm, THEN add 2.5ml/gallon of Cal Mag Plus (1/4 strength). After about a week, bump the Cal Mag to 5ml/gallon. I always mix my reservoir to the strength of my base nutrients FIRST, then add Cal Mag. I do it that way because it's like adding back the ppm of tap water. If you used tap water you would add your nutrient strength to the ppm of your water to determine how much you've added. I feel the same with Cal Mag. It's not part of the PPM equation for the nutrient schedule.
Good luck, you're setup looks nice and clean and the plants overall look happy. Remember that the plants must adjust when you make increases. So don't jump from 1/4 strength to 1/2 strength, to full strength, that will certainly lead to burns and problems. Bump it up by a sound # each week. So if 1400ppm is the goal, you won't be there until ~ 1/2 way through flower, that's the peak. The easiest way is to take the final PPM and just divide it by the # of weeks you are going to be growing to get there. It's not exact, but it gives you an idea of how it should be going. If along the way the plants look hungry or overfed, adjust accordingly. So from seed to 1/2 way through flower is about 12 weeks. I don't start feeding until the seedlings are 2 weeks old, so call it 10 weeks. I usually aim well below the feeding schedule for something around 1000ppm. 10 weeks, 1000ppm, 100ppm/wk avg should do the plants very nicely.
Remember, nutrients don't make your plants grow faster. When they have adequate access to what they need, they grow optimally, when they have too much, or too little they start showing you signs. If you want the plants to grow faster, buy a bigger light or find different genetics, force feeding doesn't work.
