Balanced fish pond: Healthy tilapia swim in clear water while stagnant water is shown on the other side.

Is Liming Your Fish Pond a Waste? What You Need to Know About Water Alkalinity

Rhea Morgan in Science & Nature August 2025 • 4 min read.

"Uncover the truth about using sodium carbonate (Na2CO3) in Nile tilapia farming and whether it actually boosts fish growth. Hint: it might depend on your water's current state."

For fish farmers, maintaining optimal water quality is crucial for healthy fish and good growth. You probably know the basics: keep an eye on dissolved oxygen, pH, and ammonia levels. But what about alkalinity and hardness? These two often get less attention, yet they're key indicators of water quality.

Alkalinity acts as a pH buffer, preventing drastic swings that can stress or even kill your fish. Hardness, on the other hand, refers to the concentration of minerals like calcium and magnesium, essential for various biological functions in fish. Liming, the addition of alkaline substances, is a common practice to improve these parameters, but is it always effective?

A recent study investigated the impact of liming with sodium carbonate (Na2CO3) on Nile tilapia, a popular aquaculture species. The goal was to determine if this type of liming improved water quality and ultimately boosted fish growth. Here's what they found and what it means for your fish farming practices.

The Liming Experiment: Na2CO3 and Nile Tilapia

Balanced fish pond: Healthy tilapia swim in clear water while stagnant water is shown on the other side.

Researchers at the Universidade Federal do Ceará in Brazil conducted a six-week experiment with Nile tilapia fingerlings. They wanted to see how adding sodium carbonate (Na2CO3) to the water affected both water quality and the growth of the fish.

They set up 24 aquariums, some indoors and some outdoors, with different water conditions: clear water (without much algae) and green water (rich in algae). They then tested three different water management approaches:

No treatment (the control group)
Acidification with hydrochloric acid (HCl)
Liming with sodium carbonate (Na2CO3)

The researchers carefully monitored several water quality parameters, including ammonia levels, calcium hardness, pH, and total alkalinity. They also tracked the growth of the tilapia, measuring their weight, length, and overall biomass.

The Verdict: When Does Liming Actually Work?

So, what did the study reveal? The key finding was that liming with Na2CO3 didn't significantly improve tilapia growth when the initial total alkalinity of the water was already above 20 mg CaCO3/L. In other words, if your water already has a decent buffering capacity, adding more alkalinity through liming might not give you any extra benefit.

The researchers also observed that in green water aquariums, total ammonia, calcium hardness, pH, and total alkalinity were all higher compared to clear water aquariums. This highlights the complex interactions within pond ecosystems and how algae can influence water chemistry.

The study suggests that before you start liming your fish pond with Na2CO3, it's crucial to test your water's total alkalinity. If it's already above 20 mg CaCO3/L, you might be better off focusing on other aspects of water quality management, such as maintaining proper oxygen levels and controlling ammonia buildup. Sometimes, less is more!

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.4025/actascianimsci.v32i3.8510, Alternate LINK

Title: Growth Performance Of Nile Tilapia, Oreochromis Niloticus, Fingerlings Reared In Na2Co3 Limed Waters

Subject: Animal Science and Zoology

Journal: Acta Scientiarum. Animal Sciences

Publisher: Universidade Estadual de Maringa

Authors: Marcelo Vinícius Do Carmo E Sá, Davi De Holanda Cavalcante, Renan Loiola Barros

Published: 2010-09-03

Everything You Need To Know

What is the importance of water alkalinity in fish farming and how does it affect the fish?

Water alkalinity acts as a pH buffer in the water, preventing drastic shifts that can stress or even kill fish like the Nile tilapia. The study indicates that liming with Sodium Carbonate (Na2CO3) is not beneficial if the water's initial total alkalinity is above 20 mg CaCO3/L. Therefore, understanding and monitoring water alkalinity are essential for effective fish farming, as it directly impacts the health and growth of the fish.

What was the primary purpose of using Sodium Carbonate (Na2CO3) in the study, and what was its impact on the fish?

The study used Sodium Carbonate (Na2CO3) to test its effect on Nile tilapia in a controlled experiment. The researchers added Na2CO3 to some aquariums, while other aquariums served as controls (no treatment) or underwent acidification with Hydrochloric acid (HCl). The study aimed to determine if liming with Na2CO3 could improve water quality and consequently boost the growth of the Nile tilapia. The results showed that Na2CO3 only had an impact when the initial alkalinity was low.

How was the experiment designed, and what parameters were monitored during the study involving Nile tilapia?

The experiment used Nile tilapia fingerlings in 24 aquariums, divided into indoor and outdoor setups. The researchers tested three different water management approaches: no treatment (control group), acidification with Hydrochloric acid (HCl), and liming with Sodium Carbonate (Na2CO3). They monitored ammonia levels, calcium hardness, pH, and total alkalinity, alongside the growth metrics (weight, length, and biomass) of the Nile tilapia. The primary objective was to determine whether adding Sodium Carbonate (Na2CO3) would improve water quality and enhance the growth of the Nile tilapia.

What is liming, and why is it commonly used in fish farming, and when is it most effective?

Liming is the process of adding alkaline substances to water, often to improve water quality parameters such as alkalinity and hardness. Alkalinity helps buffer pH, protecting fish like Nile tilapia from rapid and potentially fatal pH changes. Hardness, linked to minerals like calcium and magnesium, is also vital for various biological functions in fish. According to the research, liming with Sodium Carbonate (Na2CO3) is effective when the initial water alkalinity is below 20 mg CaCO3/L.

Why is understanding and managing water alkalinity so important in the context of fish farming, and what are the practical implications of the study's findings?

The significance of water alkalinity lies in its crucial role as a pH buffer. This buffering action is vital for aquatic life, particularly for species like Nile tilapia. Drastic pH changes can stress or kill the fish. The study's conclusion suggests that if the water already has sufficient alkalinity (above 20 mg CaCO3/L), the addition of Sodium Carbonate (Na2CO3) through liming won't offer additional benefits. Monitoring and managing water alkalinity is therefore a key aspect of successful fish farming.