I have a 22 liter Ciano tank with a 20-40L ciano CF40 filter. In the tank I have 4 calico goldfish 2 large 2 small, and a golden loach. They have always been of great health I keep up with filter and water changes, I have recently planted my aquarium and it seems to be bringing up a few problems. I’ve already lost one fish (but he was pretty unhealthy when I bought him because of improper care at the pet store, he lasted a good while longer than we anticipated). I made sure that the nutrient substrate I used has been properly covered by just over 2 inches of gravel and I did daily 75% water changes for the first week to make sure the fish weren’t being affected by any substrate that may have released as the gravel and such settled. As of now, 4 weeks later, I have made only 1 water change per week and they seemed to be doing well until today when one of the smaller fish has stayed in the corner at the top of the tank only moving every so often and I’ve noticed he’s not eating as well (and also has always seemed to gulp bubbles every time he tried to eat incase that helps) but now seems and if he’s isn’t even opening his mouth when trying to get eat. I have done a complete water change in the hopes this would improve but it doesn’t seem to have affected him. It has only been a few hours since the water change so should I just wait it out in hopes he will improve or is there something else I should be doing?