ive concluded im going to have to get great white ...

it looks like a build up of nutrients, but also looking at your air line/clear air line, you may want to try to get a black one or one that is not clear, what happens with the clear air tubes in dwc because light hits the tube algae builds up in side the tube and pushes dirty air into your root zone in the bucket, so if you can not get the darker air tube in your country then try to use some dark clothe to cover up the tube on the outside of the bucket where light hits, perhaps this is algae build up inside that you are finding? but to me that black is one of two things, nutrients from the bucket, or algae build up from the air tube either way i would try to fix it, or you can just sit back and see how things go