26 Jun 2019
What Causes pH to Drop in a Shrimp Pond
Written by Zach Stein

pH is one of the key water quality parameters shrimp farmers need to track. pH drops or swings can stress your animals and extended periods of time outside of safe pH ranges can put them in danger of disease, death, or ammonia poisoning.

In this post we’ll explore the daily cycles of pH and what you can do to protect against abnormalities.

The Diurnal pH Cycle in a Shrimp Pond

Carbon dioxide is acidic can unmitigated can lower pH down to 4.5. Now this rarely happens, but when aglae in the pond stop photosynthesizing at night and begin to respirate, it produces CO2, which can lead to a drop in pH.

Once the sun rises and photosynthesis begins again, the algae begins to produce oxygen again which both raises the dissolved oxygen and the pH as the excess carbon dioxide can off-gas from the surface of the pond.

The Risks of pH Swings in Aquaculture

A lot of factors can increase the likelihood of a pH swing in a pond, but one of the greatest is from an imbalance of algae and a correction. As algae concentrations are highest in the afternoon as they have had a full day photosynthesizing, they can overpopulate and a die-off can occur.

This can lead to sudden drop in pH. If pH drops by over 0.5, it can lead to your animals feeling shocked and stressed making it much harder for them to convert food into growth and increase the likelihood of disease. This is an especially high risk factor during rainy periods where the salinity of the pond will be lower and algae will grow faster.

Fast changes in pH can also be an indicator of a full algae crash, meaning the population of algae in the pond dies, both lowering the pH dramatically, and more critically, absorbing much of the excess dissolved oxygen in the process.

How to Protect Against Changing pH

Watch the weather, check your pH at least twice a day, and track your alkalinity closely.

The best defense against swings in pH is maintaining healthy alkalinity levels. Alkalinity buffers against swings in pH. So ensure that your ponds are correctly limed to avoid unnecessary stress to your animals.


Fast changes in pH are more likely to occur when the salinity is changing in the water and algae levels are building. Make sure your ponds are buffered against changes and track them closely.