Came home and noticed my SA cichlids weren’t excited to see me so I opened the lid and to my surprise the water smells rancid.. the nitrates are through the roof but nitrites and ammonia are normal. Doing a 50% water change and took out all the plants(which smelled nasty) and the rocks. Even with the new water being added(tested and good) it still smells. My cichlids are stressed out and so am I!! Help!!!