Hi Everyone, I got a call from my friend last night after he tested his water params before routine cleaning. These are his readings: ammonia 0, nitrite 0 and nitrate 40. The week before, the nitrate was at around 15. I suggested that since he was testing before a routine cleaning, that he make sure to vacuum his gravel thoroughly because he does tend to overfeed a bit. I went over to see how much waste was actually in the gravel. While looking around his tank, I noticed something between the leaves of a plant. It was a very fuzzy congo tetra that he had not seen for a few days. I know that a dead fish that is left in the tank can cause the ammonia to spike but can this be the reason for the rise in nitrates with a 0 reading of ammonia and nitrites?