Agree with the above, the amount you are changing is not nearly enough to keep your tank from being an HITH disease soup.200L out of 1400L is about 14% water change, possibly less as the tank is probably not full to the rim, and substratum and decorations occupy a lot of volume. So you may be changing about 10% weekly, or even less. IMHO that is way too little. I would not be comfortable changing any less than 50% weekly, ideally substantially more (50% twice a week?). You have some very nice fish and what looks like a very nice setup.
Good luck!



