powdery mildew, salt buildup?

Whats up people? This is the first run with this hydro system & Im having a little problem well not a problem yet i dont think. I have noticed white stuff on my 4x4 rockwool cubes. my system is a recirculating NFT system using 5 gallon buckets, 6" net pots filled with clay pellet around the rockwool cubes. I have drippers dripping onto cubes & 4" coco covers over rockwool.
Anyhow the plant look great no signs of stress so im really only concerned about the white shit building in the cubes & stones. There are no signs of powdery mildew on the leaves anywhere. Its just on the rockwool & stones right now. I thought it might be salt build up but the stuff wipes off rather easily. I'll try to post a video or pic in a moment. thanx in advance.....

I would try to cover the rockwool with rocks, or plastic and move your dripper off to the side of the cube, looks like salt buildup and from light, I would flush it with something like final phase. Good luck to ya happy growing

If it is on the pebbles also, I would say salt. Mildew will not grow on clay, or rockwool. It needs an organic food source. If is on the leaves, then you have issues. I would just use water with a low dose of nutes and peroxide mixed in and give the rockwool a good soak from above. Make sure you have good airflow around your plants also. Good luck

Thanx guys for the replies, I had a guru buddy of mine come over & he said it was salt buildup. I got a little nervous at first but the plants had no sign of mildew on the leaves. anyhow thanx again guys....