sprouts: welcome and enjoy growing. a tip on lights:
its almost always better to upgrade to a higher wattage, instead of adding another lamp. this is because adding another lamp and ballast increases the heat but not lumens. (a second 50w lamp will only increase the amount of light coverage on the plants. lumenosity, the total amount of lumens available to the plant don't actually go up by adding another lamp.)
also, try to keep a 50w within a foot of the main cola. HPS gets 105 lumens/watt, so 50w = 5,250 lumens (appx) but that is counted one foot away from lamp. at two feet lumens drop to 1,300, less if it has to penetrate foliage. 7,000 lumens over the whole plant seems to be the desired range for vigorous growth. thats a 150w or higher for a good 2' zone of high lumenosity. you cant do it by adding another 50w.
by the way, i use mirical grow regularly and have no problem with nutrient lockout or anything. use should not have a need to flush with every watering. mirical grow with the feeding granules is the one you want to avoid because we want to feed the plant everything it needs.
hope this helps. good luck.