Hi, I'm new to fish keeping and purchased an amazon sword 3 months ago. Currently, there are five guppies in a 20-gallon long tank. It has been set up and going for about 5-6 months now. I have missed a couple of water changes, but lately, I've seen my amazon sword leaves starting to turn brown a die off. I'm fertilizing with Seachem Flourish about once a week. Can you please help me figure out why this is happening? I am not having excessive algae growth, and the LED lights are on for 9 hours a day.