Do you ever siphon off the bottom where the detrius is? A build up of all that waste will raise your ammonia and nitrite levels. Even nitrate levels can effect health if high enough.
The other problem I can guess at is that orandas prefer cold water. Higher temps do effect their swim bladder and can cause fungus to develope in their wens. Orandas thrive best at temps around 60-65 degrees. You may need to bring them in.
As a side note, I bet your plants go wild with that tank water!