Thanks guys. I realise now that I need another tank. What would be the priority i.e. get more discus (& will my 200l cope short term) to stop the bullying or get another tank & deal with the compatibility & temperature problems? Sadly I'm not going to be able to do both immediately.
Thanks for all your help.
Adding to the group of discus would be wise, as it would help alleviate stress issues, and would lead to the group of fish collectively being healthier. When I first got into discus, I brought home a single fish, two more the following day, a fourth later that week, and finished the group off with another 3 about 2-3 days later. I then returned 1 of the discus, who was being singled out and seemed very timid in the group. I've had 6 happy discus since, and 2 of them have even paired off and have begun spawning. That being said, it may be wise to consider investing in the secondary tank soon if you plan to keep the corys, tetras, and gouramis in cooler water than the discus tank. The discus, especially if they are young, (speaking of which, how large are they?) need warm water. I keep my 55g (208L) discus tank at a steady 31c.
There are always going to be anomalies to whatever statistics we can get a hold of, and there will always be the one person who says that you can get away with something that everyone disagrees with. I'm not going to take either side, I'm merely going to share my experience, and let you take it for what it is worth. I purchased 6 corydoras (3 spotted, 3 peppered) for my discus tank a little over 3 months ago. (this is when I kept the tank at about 29c) I took about an hour and fifteen to acclimate them, being careful to slowly raise the temp of their water. I had one die overnight, the other 5 are doing well to this day. Now, these are catfish, living in water which is 88 degrees fahrenheit, or 31 degrees celcius. According to just about everything I'll read online about them, they're really only meant to be in water up to 25c. I'm pushing the envelope by 6 degrees celcius, which is quite a lot for a fish. Am I trying to kill them? Absolutely not. I genuinely enjoy my corydoras. I cannot see how their internal organs are being affected, so I very well might be on here in a few months posting that I was wrong about keeping cory's with discus, but for now, they appear to be doing very well. They are active, have good appetite, and tend to stick together for the most part. I'm not going to tell you whether you should or should not have corydoras with discus, I'm just sharing that I'm doing it, and in the 3 months I've had them (which really isn't very long, when compared to their 5-7 year life expectancy) they have been acting as though they're healthy and happy.
