please help!!

hey guys im new here and im doing my first hydro grow. some of my plants looks a bit yellow and some of the tips are brown i had to add some ph down and the ph is 7.0. my clones are about a week and a half. should i flush them with pure water and have them only running on water for a couple days then do a half strenth solution? some help would be much appreciated. thanks

1.https://www.rollitup.org/marijuana-plant-problems/132382-deficency-nute-burn-diagnostic.html

http://images.google.com/imgres?img...tomato+leaf+chlorosis+picture&um=1&hl=en&sa=X

thanks alot i flushed them with purified water and i lowered the ph to 5.8 and there on only water now for a day of 2 and that seems to be working