Are you adding CO2 to the tank? if not try API CO2 boost 5-ml per day in a 10 gallon set. 1-ml per day in smaller tanks. Also it kind of looks like a fertilizer burn so you may be adding to much flourish. I have noticed the same type of problems in many aquarium shops. I know they don't do anything besides put the plants into the tanks and wait to sell them. What type of substrate do you have. Does it contain Iron and minerals?