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My dwc setup smells 'wet' or moldy

Hi all,
Its been exactly a week since I setup my dwc. Everything is going fine. The roots are a little brown but they were brown from when it was transplanted from dirt. The new root growth looks very nice and white with little hairs and stuff.
The plant is only small, I was going to change the water next week, although some suggested for a seedling you can get away with a month. Anyway I started this thread since I am a paranoid bastard and don't want to view any of the MJ threads on my computer.
My bucket smells wet, moldy, mildew. I don't know how to explain it but its that smell of water sitting in the sun, a wet towel which has been wet for a while. It smells earthy and I suspect its mold. Thing is there is absolutely no signs of mold. The water is crystal clear, the roots don't have any slime build up, the bucket is only small(13L of solution with a big 5" air stone and 200L of air going in). I was concerned about the temps but 3 separate measurements, 23, 22.5, 21.1. The bucket is black, it does not get anything but morning and afternoon sun. The solution I use GH flora bloom and micro. The PH is about 6. The PPM's are blind, I just followed the seedling guide on the label and .75 the suggested amount.
Just this smell. I can't get my head around it. If I just touch the lid to open the bucket, my fingers smell and I wash them straight away. I've dumped a little h2o2 in there, talking 30ml which probably isn't enough for anything. I need to get some of the heavy duty 29 - 35% stuff and from what I've read its 3ml to 4L of water, so I'm looking at 9ml.
Part of me suspects it might be normal. Usually where you find plants and moisture, this smell is there. If it can be eliminated or something done differently to reduce/nullify the smell, I'm all for it.
Also when people talk about roots in dwc how they should be white, will old roots turn white or is it the new growth which will show if its doing well or doing bad? My plant hasn't put any growth on up top but it looks like all energy is being spent on the root system.
If I wanted to clean out the bucket, would sitting the roots in matching PH water(or the same water in a different bucket) be fine while I clean out the old bucket? Would it stress the plant if I was to gently wash the root system with flushing water?
Can get pics of the reservoir if needed.
Cheers all.