Hello everyone!
I am very happy for finding this site today, everyone is really helpful and passionate about keeping healthy fish in harmony with their environment. So here is my problem.
I had a wonderful tank that was established for 2 years with 5 fish, a frog, and living plants. It was perfect, I had all my original fish, I never had to do a restock. Then disaster struck, when I returned from my honey moon I noticed the fish were acting really lethargic and that their fins were all stringy. I did a water test and every reading was off the chart. I did a fast 50%
water change and did my best to get things back to normal but they didn't make it

. My first question is, in a span of 6 days what could have happened? I had my light on a timer, I cleaned and Vacuumed the tank, I tested the water a day before I left and every thing was Ideal. I had a friend of my house sitting and all he did was feed them.
So now I am starting a fresh water tropical and it has been just over a month and I am in a rut. My
nitrite levels have declined from off the charts to 5.0 to 3.0, my other readings are ideal but these high levels of Nitrite will make living conditions in my tank stressful if not fatal. I have added
API Stress Zyme, a Biological filtration booster. I have added this as directed from the bottle, but there is no change in my readings. So any input on how to bring my tank under order and bring these Nitrites down?Thank you all for your help and support.