This is due to the relationship of Alkalinity and copper. Copper ions can be more toxic to fish if the alkalinity is below 50. A good range of alkalinity level is between 100-180 mg/L (ppm). A maximum suggested range is between 100 – 250 mg/L (ppm). One easy way to raise low alkalinity is to use ordinary baking soda. Adding ¼ cup (0.15 lbs) per 1,000 gallons will typically raise the alkalinity by 10 mg/L (ppm). Raising the alkalinity should not be done all at once, but over a period of days.