Try running without the spreader. My instinct says the root of the problem (har har har) lies somewhere between the block and the tray... roots will naturally grow to the best area available to them, and don't need guidance.
stinkyattic Reviewed by stinkyattic on . brown roots? but not root rot!!! have nft.canna aqua vega 1.2 cf, ph 5.8, tap water ( been tested ok ). about a week after being put in the tank the roots under rockwool block turn a sort of translucent brown and are weak, but do not go mushy, roots outside of block are white but eventually go the same. plants still take up water, but growth is very slow. stem go's purple and older leaves, then others yellow suggesting slow,or no neut up take. everything is always sterilised and rinsed, but this has happened 3 times in a row. Rating: 5