Something is bothering me, for the actual aquarium, I took back the gravel from the old aquarium which is absolutely the same, similar filtration, I just added a nutritious soil aquabasis+ in the new one. There were dead fish, the day I took out the gravel, one fish was gone, he was dying, I probably mixed it in the gravel even though I didn't see it, is it possible that decomposition is the cause of that, it's been at least 8-10 weeks ? I'm probably going very far, but I'm trying to understand where this imbalance comes from.