Balancing pH Levels in Freshwater and Saltwater Aquariums


Using a scale of 0 – 14, pH strips test the chemical levels in water. In general, a score of 7 is considered neutral and most fish thrive in a pH of 6.4 – 7.8. Finding the right balance of chemicals is essential because low pH is highly acidic and can burn fish, while higher pH balances feature high doses of alkaline which chaps the skin. The best way to ensure a long life for your fish is to consistently maintain pH balances, not allowing them to significantly change at any point.

pH Levels in Freshwater Aquariums

In general, freshwater fish aquariums require a neutral pH balance. Choose a balance between 6.4 and 7.8 and your fish should thrive. The hard part is maintaining that balance. If the pH balance changes more than 0.3 units in a single day, it can cause the tank’s inhabitants to enter what’s called “pH shock.” pH shock is potentially fatal, so avoid significant increases or drops in pH levels. It’s a better idea to acclimate your fish to a higher pH than a lower one because pH levels will lesson overtime. Rocks and substrate influence a higher pH level, as does increasing the oxygen concentration in the water, as this will decrease carbon dioxide and thus increase pH levels.

pH Levels in Saltwater Aquariums

Saltwater tanks require slightly higher pH to function normally. Measure this pH balance daily, to ensure that levels are consistent and not dropping. As with freshwater aquariums, significant changes in the pH balance can yield disastrous results, such as death. For fish-only tanks, choose a balance between 7.6 and 8.4. For reef tanks, choose a pH balance that’s slightly higher, between 8.0 and 8.4. If pH balances ever dip too low, add baking soda or a commercial product that’s designed to increase levels. If the pH is ever too high in a saltwater tank, add some vinegar or lemon juice or a commercial product that’s designed to decrease levels.

pH Levels in Medium – Large Ponds

Before stocking a pond with fish, it’s important to determine pH levels and balance them if necessary. On average, a pond should have a pH range of 6.5 to 9.0. In order for fish to survive, do not allow oxygen levels to fall below 4 parts per million (ppm). 3ppm can potentially stress fish, while oxygen below 2ppm has been known to suffocate pond dwellers. For optimal pond production, try to uphold a total alkalinity of 20 ppm. Unlike aquariums, it’s generally okay if the pond’s pH fluctuates between 6.5 and 9, but allowing it to fall below or above these ranges can be deadly.

pH Levels in Small Backyard Ponds

Smaller ponds, like koi ponds, are going to require a stable pH level between 6.8 and 8.2. Ideally, the pond should manage a pH level of 7.5, but the real focus should be on consistency. If possible, avoid hard water in a backyard pond. A pH decreasing tablet can be added to hard water and cause a short term decrease in high pH levels, but those high levels may return after 24-48 hours. It’s best to use medium-to-soft water in conjunction with a pH-adjusting product to ensure that daily levels do not fluctuate and shock or kill the pond’s inhabitants.

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