NFT: Roots are damming up gullies causing brown roots

I am growing in NFT gullies that are 150mm wide. I put freshly rooted clones into the gullies on a 12/12 light schedule. They grow about 50cm high and have good whiteish roots for the first 3-4 weeks but then the roots go brown and when I lift up the wicks to inspect I realise that the water level is too high (10-15mm) and is drowning the roots. The only solution I could think of was to trim the roots. I am also going to raise the angle of the gullies a bit.
But it seems to me that I am going to have to trim the roots to prevent this damming effect.
What puzzles me is that everyone is using these 150mm gullies and I haven't heard anyone mention this problem. If there are wider gullies available then I would get them because I have 50-80mm (approximately) space between the current gullies.
I was thinking a perferated channel of some sort that went down the middle of the gullies could perhaps prevent damming. Like a hose with holes in it that the roots would grow over.
I wanted other peoples experiences and ideas. Has anyone else had this problem. I can't believe it's a rare occurance. Thanks yall.

 

is yer water aerated? might help!

 

have ur water trickle into your gullies ,u do not want ur gullies flooded. and are u using liquid oxygen or an air pump to to put oxygen into the water , if not do so ,this should sort out ur problem