about three days ago I changed the substrate of my running 30g tank from sand to dirt capped with gravel; resulting in all my fish -except for five small red tetras- dying over night.
As for details: I bought potting soil by the brand "Ja, Natürlich" (which means "Yes, of course" or "Yes, organic" kind of a wordplay) containing composted horse dung, worm castings and lava stone gravel.
Though the soil was full of different little stones and pieces of wood (they should definetly rethink the diet of those horsies) I decieded to use it.
I rinsed it twice, got out most of the wood, spread it thinly in my garden and kept it moist for about a month.
After filling I experienced vast turbidity, couldnt even see the back of the tank, though with my fishes beginning to try and jump out of the bucket I replanted the tank and put the fish back in on the same day.
So the next day I woke up (I think it was around 2 p.m. or smth) and find most of my fishes to be dead and those 5 ember tetras swimming at the surface. They are now in another small tank disturbing the peace of my betta female -though feelin fine.
Does anybody have any clues where I could've gone wrong? Could the percentage of organic matter be too high, therefore choking my fish overnight? Or is there a chance of anything toxic leaching from some of those little stones?
Any conclusions on how I should proceed? I really wanna try and see if this still works out without redoing my tank again; or should I try again with a different kind of soil? This is probably hard to answer, but do you guys have any ideas how i might find out what happened?
As for organic matter: I tested the water and Ammonia is zero, Nitrite is abit high its 0,025ppm and Nitrate is about 20ppm so theres no issue here yet. Though my test set is pretty old so I cant say if those measurements are exact or anything
heres a (bad) pic of the tank now.
and one (even worse) before planting etc.
thanks in advance for any advice I really did not expect this
btw: I just found out apparently there is charcoal dust in there as well could this be a reason too?