oranda acting differently after water change

Question
Hi,

a few weeks ago i purchased an oranda and a blackmore fish. once in their tank both were swimming what i thought was normally, although after reading found what seemed to suggest that the oranda was swimming erratically,  and there was limited to no hiding. after one week i did a water change after reading that the orandas swimming was a possible ammonia problem. the water was treated and the same temperature as the tank (give or take 1 degree). i also cleaned the filter in the water that was taken out, it was also not a complete water change probably 40% at the most. after that both the oranda and the blackmore have been swimming close together and now the oranda will only swim when there is food or my hand in the tank, and this is very scared erratic swimming (nothing like before)other than swimming for food it is hiding in the plants, but will move when i go over and take the lid off. After the water change if anything the blackmoore has been more active then before swimming more and scouring the bottom for food. there has also been high temperatures here in the UK over the last week/weekend before the water change, and I am  not sure if this has had any effect on the oranda.

sorry about how long this is and thanks for any help

Answer
Susan,
When you bought the tank, did you cycle the filter before you added the fish? Are you doing complete water changes at all? If you are, stop. Every time you do that, you send the filter back to cycle mode. This will harm your fish. Hopefully, you have you two goldfish in a tank no smaller than 30 gallon, with a filter for a larger tank. You Black Moore is more active after a water change because you are removing the deadly ammonia and nitrites that are in the water. Using an API liquid water tester, test your water weekly for ammonia, nitrites, and nitrates. Ammonia and nitrites have to be at zero at all times. If either one of them is registering higher than zero, do a water change. Test every day until the ammonia and nitrites are back at zero, then test once a week or sooner if the fish look like they are stressing.