the white material is the spreader mat, yes it is nutrient film tech. i don't think it's light because the roots go brown under the block first . roots inside block seem to be strong and healthy. been to my local hydro shop and they say that the solution should be adequately oxygenated in my system. but i have been adding liquid oxy (ie oxy plus) at 5ml per 10 litres. i also add pythoff. ph of solution is 5.8.
solution temp if i had to guess would be room temp/ tepid but not warm. when you say desiccated do you mean dry? because they don't feel dry. as i have said i have discussed my problem with my local hydro shop and they are totally stumped!!!