Colin_T
Aquarium Advice Addict
I would say it's the gravel. Filters won't cause ammonia to go up to 8ppm unless they are full of dead fish or fish food. Black silicon or any aquarium silicon won't cause this. You removed the moon rocks and the only thing left is the gravel.
Get 2 buckets of tap water. Test the pH and ammonia in both buckets. Add a few inches of gravel to one bucket and leave the other bucket with just water in. Monitor both buckets for pH and ammonia over the next week. If the bucket with gravel gets an ammonia reading, that is the problem. It would also explain the white slime that grew on the substrate. I reckon you got a bad batch of gravel.
Get 2 buckets of tap water. Test the pH and ammonia in both buckets. Add a few inches of gravel to one bucket and leave the other bucket with just water in. Monitor both buckets for pH and ammonia over the next week. If the bucket with gravel gets an ammonia reading, that is the problem. It would also explain the white slime that grew on the substrate. I reckon you got a bad batch of gravel.