New Box, finally

yeah man change the light to 20 hrs on 4 hrs off.

water every day, maybe only give feed every 2nd day. ive done it that way before no problems.

did u flush the coco out before using? some of it comes very salty. coconuts grow on the beach and heaps of processors dont flush it. it also helps to soak it overnight in pH adjusted 1/2 strength nutrient to pH buffer the coco before planting.
id give em a really good flush, like 5 litres each or a gallon each whatever yr measurements are. and then feed em.
make sure they drain freely and dont sit in wet trays.
keep yr ventilation going all the time. you can rareley have too much air exchange, just as long as the leaves are dancing and not being blown like a tornado.
the fans + the fluros use fuck all power.
when i ran a 400w hps it cost me in australia $40 for 3 months inc fans.

hopethis helps. all the best.