could be calcium deficiency.. when this happens your leaves turn brown on the ends or just cripple slowly but still live..

--to fix this problem get some hydrated lime and add about 1 tsp per gallon of water you use..

could be magnesium deficiency... to fix this add about one tsp of epsom salt per gallon of water you use..

make sure stuff is disolved, use hot water..

also, make sure water is right PH.. I Reccamend distilled water, works the best!