I have sort of the same problem...except without the algae and dying plants. I've been doing a 50% water change very 3 to 4 days to control high nitrates. In my case I believe it to be overstocking (I'm not familiar with your fish so I can't say in your case) and root tabs. Have you checked to make sure you are not overstocked?
Do you use root tabs?
Do big water changes. Clean water will help your fishes heal. I understand those big water changes are a pain in the butt.....but those water changes will keep your fishes alive.