That's definitely what that is and if you don't flush with just PHed water it will continue by your leaves turning yellow and eventually causing necrosis and ultimately ends up killing your leaves. The damage done with the yellowing and necrosis is irreversible but you can get your plant stable and have her rebound. Right now you have what they call a "light cawl", but if you fix it your plant will recover where the green is. Like I said flush with just PHed water and check your PH and EC/TDS/PPMs and once stabilized start your nutrient regiment at half dosage and move back up to normal gradually.