After adding Fluval natural gravel to my soft water tank, the pH level spiked. Should I remove the gravel?
Due to the low KH value of your soft water, the gravel increased the buffering capacity of your water (KH) and, therefore, the pH value as well. Keep an eye on your fish and perform a few extra water changes while using a product (i.e. Nutrafin pH Adjust Down) to help lower pH if necessary. They will adapt to this pH and, in fact, it will be far more stable from now on.