Water changes with sump - how often and how much?

I have set up a new Planted 4ft Discus yank 2 months ago, 6 x Discus added 2 weeks ago after the tank had cycled. It also has 7 x Cory Julii and a few Cardinal Tetras. The tank is approx 220 litres with a separate 30 litre sump. I made a 40 litre water change after the 1st week but the fish were not happy, all sitting at bottom of tank but then the following morning they were ok. I purchased fish from Nick at Sydney Discus World who appears to be very knowledgeable and was told NOT to make any further water changes for at least another 2 weeks and then to only change no more than 10% water weekly, preferrably fortnightly. I do not want to do anything to harm these fish and I am confused, hearing so many stories of people who change up to 50% water weekly which also seems excessive. Today 1 of my fish is only breathing from 1 gill at a time. Can this be due to water conditions?
Can anybody help?.

Hi again Steele,

Good to see you have made it here. To get the most of the experience available here you should also add information regarding your water conditions and measures, ie, pH, gH and kH. Measures for ammonia (your LF post indicated .5), nitrIte and nitrAte.

There is nothing more I can add to what I suggested to you in response to your LF post.

Regards,

Bob

Hi Bob, THANKS for your reply. The pH is 6.4 Ammonia is .25 Nitrite 0 Nitrate .20 I have been told that Ammonia cant harm fish if the pH is under 7. Can that be correct? That is why I was told not to change water for another couple of weeks. Sounds strange?
I have also been told NOT to worry about testing water for hardness in Sydney metro so I have NOT and do not know what the gH and gH are. Should I get a test kit for this also? Any advice would be much appreciated

Reposted with updated information - I have set up a new Planted 4ft Discus Tank 2 months ago, 6 x Discus added 2 weeks ago after the tank had cycled. It also has 7 x Cory Julii and 8 x Cardinal Tetras. pH is 6.4 Ammonia .25ppm Nitrite 0 Nitrate .20ppm The tank is approx 220 litres with a separate 30 litre sump. I made the 1st 40 litre water change last week but the fish were not happy, all sitting at bottom of tank but then the following morning they were ok. I purchased fish from Nick at Sydney Discus World who appears to be very knowledgeable and was told NOT to make any further water changes for a month and then to only change no more than 10% water weekly after that, but preferrably only 10% water changes fortnightly???. Its been 2 weeks and 1 fish has started to breath from only 1 gill. Can this be due to water conditions? The shop I got them from says it will NOT be gill flukes but I am concerned. I do not want to do anything to harm these fish and I am confused, hearing so many stories of people who change up to 50% water weekly which also seems excessive.
Can anybody help?

Increase the w/c 80ltr everyday this will help with the gill issues,increase the air ration in tank,increase temp 30 deg this should help your discus to recover in a couple of days.Ammonia will kill your fish & don't worry their are people here to help with more than enough experience,MOST of all don't buy from nick,their are breeders on here who sell top quality & disease free discus at a better rate than Sydney discus world

Hi Steele, and others,

I found this to be of some interest and perhaps useful.

http://dataguru.org/misc/aquarium/AmmoniaTox.html

Would like to hear from others regarding potential/validity of this data.

Regards,

Bob

Thank you very much for the replies. I found the table on Ammonia & Ammonium very interesting. I presume that is why Nick from Sydney Discus World has been telling me not to worry about Ammonia, he also said at a pH of 6.4 and water temp at around 28 - 30 degrees that any Ammonia becomes Ammonium and is not toxic to fish. He also keeps telling me NOT to make any water changes for at least another 2 weeks, maybe thats also because he is not worried about the Ammonia - he keeps saying the fish need to get used to the new water first and because tank is relatively new. 2 days ago I did a small 10 litre water change and topped up another 8 litres, then I checked the pH 6.4 Ammonia .25ppm, Nitrite 0, Nitrate 20ppm. Today I checked again and the pH 6.4 Ammonia .50ppm Nitrite 0 Nitrate .40ppm. Because the Ammonia and Nitrate readings had increased I called Nick ( Syd Discus World ) and he said NOT to change any water as tank was still new. The tank was set up on 03 January and on 10 January I added driftwood plants, tetras added on 14 January to help cycle tank. From 22 January I began to get 0 Ammonia readings so it appeared tank had cycled, however I did NOT add Discus til 11 March. So now I am still confused. Should I disregard Nicks advice and start doing water changes immediately or should I wait another 2 weeks. Really apprecaite your thoughts and advice? Thanks

I will also make a new post for this - The discus that had white spots apparently has a parasite disease, I took it back to Syd Discus World. Very interesting - For 2 weeks 5 fish were put into a tank together at the shop to get used to each other, the 6th fish was not but was added to my tank the same day/time as the others. The 5 fish that were already together settled in fine, however they all kept harassing the other fish constantly which then set off some sort of pattern and all the fish were not happy, the largest would hassle all the others, the 2nd largest would hassle all the others except the largest fish etc. and for 2 weeks it did not stop. And then ALL the fish used to gang up on the new one. I decided to take the sick fish out of the main tank and put him into the large sump and almost immediately all the fighting stopped. Now the 5 remaining fish are happy - they all know their pecking order and everything seems good. I really don't know if its a good idea to bring the other fish back. Any thoughts or advice would be appreciated.