hi, i use clay pebbles and have a 4 pot wilma, the pebbles were not as clean as they should have been when i started and did have white dust on them. ive been getting white powder floating on top of the water in the tank, its coming from inside the pots. i gave them a big flush in the shower last week(an cleaned room an system), the drainage looked like milk at first but ended up clear after 20mins each pot. they started growing again but the problem is coming back, im on week 4 of veg because they are growing slowly and about the size of my fist, with 4 nodes on(used seeds), ive already lost 2 of 8 plants and its looking like 3 of 8. need help man. whats my next move?