What Are the "Old Three" in Fish Keeping? This Article Explains It Clearly

I often tell fish keepers who come for advice that they can take the "Old Three" measures, but we often overlook the fact that many fish keepers have no idea what the term "Old Three" even means. Simply put, it refers to just these three methods: raising the temperature, adding salt, and changing the water. This has always been the first choice for the prevention and treatment of early-stage fish diseases and is widely circulated among fish keepers. But some may question this: are these really worth mentioning all the time? They might think it is some kind of universal cure-all, yet it truly is universal in a sense, because when fish have problems, these three operations are almost always involved.

Can the "Old Three" really be solved so easily with just "changing water, raising temperature, and adding salt"? Actually, that is not the case. We need to understand the principles behind these three operations and why we do each step, approaching and learning them with a mindset of seeking knowledge and healing. Many fish keepers are very cautious about using medication, never using it unless absolutely necessary, and instead achieving very good results through conservative treatments like the "Old Three." There are countless such examples. So today we will focus on this magical "Old Three."

01

Step One: Changing the Water

The quality of the water directly affects the normal growth and development of fish. Changing the water in a fish tank serves to clear away dirt in the water, maintain water cleanliness, regulate water temperature, increase oxygen in the water, rapidly dilute bacteria and toxins in the water, and reduce their harm to the fish. Compared with raising the temperature and adding salt, changing the water does the least harm to the fish and works the fastest. Especially when the nitrification system has not been fully established, toxins exceed the standard, or the water is extremely cloudy, changing the water is almost the only choice. Water changes in the "Old Three" do not mean a one-time change, but rather continuing over a period, changing the water every other day. For the amount of water changed each time, the common recommendation in China is generally between 20% and 30%, while many foreign publications suggest that each water change should be between 50% and 75%. I support large water changes because they work quickly and help sick fish more, but tropical fish require caution when changing water in winter. The temperature difference caused by large water changes can be counterproductive, and adding warm water can also be used.

When changing water, attention should be paid to: temperature, chlorine content, and pH control. The temperature of the new water should preferably be 1-3°C higher than the water in the tank. Never add a large amount of cold water, as a drop in water temperature will cause many problems. Chlorine control is very important. If conditions permit, aging the water is of course best, or using water from a water heater. Proper use of a water conditioner is also a good way to remove chlorine. The pH change with each water change should be less than 0.3, otherwise too great a pH change can cause acid-base imbalance in the fish's blood, metabolic disorder, and worsen the fish's condition. Therefore, it is very necessary to have an accurately calibrated pH pen. In short, as long as temperature, chlorine content, and pH are well controlled, the impact of water changes on fish is very small. In addition, after a large water change, salt should be replenished to prevent osmotic pressure fluctuations.

Note: In routine management, we should try to avoid changing all the water in the tank. Because the fish have already adapted to the water quality in the tank, changing all the water will suddenly alter the water quality, making it difficult for the fish to adapt, and the established aged-water environment will also be damaged as a result. There is a lot of knowledge in changing water for fish keeping, and this is a very important reason why many beginners cannot keep their fish alive.

02

Step Two: Raising the Temperature

Many people believe that the purpose of raising the temperature is to kill bacteria by increasing the heat. This understanding is completely wrong. Because the vast majority of pathogenic bacteria are resistant to high temperatures, their optimal growth temperature is generally around 37°C, and the upper limit for raising the temperature in a fish tank generally does not exceed 35°C. This temperature is the optimal reproduction temperature for bacteria and will not harm pathogenic bacteria at all. Raising the temperature not only fails to sterilize anything, but as the temperature rises it can also cause pathogenic bacteria to multiply in large numbers and increase their toxicity, worsening water quality. This is a truth that anyone with even a little common sense understands. So, is there any scientific basis for raising the temperature? Is raising the temperature timely help for sick fish or adding frost to snow? We should think about this question carefully.

The Principle of Raising the Temperature

To understand the true purpose of raising the temperature, one must understand the fish's immune system. Fish are ectothermic animals, and this physiological characteristic determines that fish do not have the ability to maintain a constant body temperature. The body temperature of most fish is the same as the surrounding environmental temperature. The fish immune system is closely related to temperature. At low temperatures, immune function weakens, making fish death more likely. When disease invades, the fish itself will show symptoms of "fever," indicating that they want the water temperature to rise.

The real purpose of raising the temperature is to stimulate the fish's immune system and increase the fish's metabolism to fight off invading pathogens and toxins, not to directly sterilize through those three to five degrees of warming. Of course, there are exceptions to everything. For example, the small ich parasite that causes white spot disease is directly killed by raising the temperature. In disease treatment, the principle of choosing the lesser of two evils should be followed. Although raising the temperature may cause bacteria to multiply in large numbers and damage water quality, raising the temperature can better strengthen the fish's immune defense and enhance the fish's constitution to resist disease. For sick fish, this is crucial.

The Correct Way to Raise the Temperature

A reasonable temperature increase should be 3-6°C above the original tank water. Depending on the fish species, this range is roughly between 30-34°C. It is best to raise the temperature by 2-3°C per day. Raising it too quickly will cause discomfort to the fish. Raising the temperature must be accompanied by strong aeration to ensure an adequate oxygen supply. This is because after the temperature rises, the fish's respiration will intensify, bacterial reproduction will accelerate, and oxygen demand will increase. Raising the temperature should be used together with salt to reduce the burden on the fish's osmotic system, which will be described in detail in the next section.

Regarding raising the temperature in the fish tank, here are a few suggestions for everyone:

1. Heater rod

Advantages: It can control the temperature, is convenient to operate, and has a relatively good heating effect. Disadvantages: Some heater rods have too much power and consume electricity.

2. Periodically adding hot water to the tank

Advantages: It can control the temperature and does not directly heat the water in the tank, making it relatively safer. Disadvantages: It is inconvenient to operate and easily startles the fish.

3. Placing a bottle filled with hot water into the tank

Advantages: Safe, and the temperature will not become too high. Disadvantages: Inconvenient, requires regular replacement, and the heating speed is relatively slow.

From the perspective of safety and convenience, ornamental fish hobbyists are advised to choose a combination of a heater rod and a temperature controller. This double protection can effectively prevent situations such as excessively high temperatures or fish death during the heating process.

03

Step Three: Adding Salt

Misunderstandings About Adding Salt

In the "Old Three," adding salt has the most misunderstandings, including both the theory and the dosage. Many people casually sprinkle a handful of salt every time they change the water, and when treating fish diseases they do not dare to add much salt, only sprinkling a few more handfuls than usual. These are all incorrect practices. Most people believe that salt can sterilize and that adding salt is for sterilization. This is an even more mistaken theory. High-concentration salt (20%) has a certain preservative effect. Due to the osmotic effect of salt, bacterial cells dehydrate and die. Salted meat and salted fish are cured according to this principle. In fact, a high salt concentration in food can only slow or stop bacterial reproduction, but cannot kill bacteria. In our fish tanks, the highest salt concentration we add is only 0.5%, which cannot achieve any sterilizing effect at all. Taking a 500 L fish tank as an example, to reach a salt concentration of 0.5%, 2500 grams, or 2.5 kilograms, of salt is needed. This dosage will not pose any threat to bacteria, let alone those few handfuls of salt casually sprinkled in.

Exploring the Principle of Adding Salt

Fish control the balance of salt and water in their bodies through osmotic regulation. The salt concentration in the body fluids of freshwater fish is higher than the salt concentration in the environment. Due to osmotic pressure, water enters the fish's body through the body surface and is ultimately metabolized by the kidneys into urine and excreted. Therefore, freshwater fish never drink water; they only urinate. If you understand this passage, it will be easier to understand the purpose of adding salt.

The purpose of adding salt is to regulate the osmotic pressure of the water, reduce the osmosis of water into the fish body, prevent viruses in the water from spreading within the body, reduce the burden on the kidneys, relieve the pressure on the osmotic system, and improve immunity. Adding salt can reduce the negative consequences brought by raising the temperature. Although raising the temperature can accelerate bacterial reproduction, after adding salt the osmotic pressure of the water decreases, which can maximize the blocking of bacteria from entering the fish's body. Therefore, raising the temperature and adding salt complement each other.

The Correct Way to Add Salt

Only when fish are sick and need treatment is it the correct time to add salt. Adding salt with every water change will reduce the fish's osmotic regulation ability, and when the fish actually become sick, the effect will be poor. This should not be done ordinarily. For salt, it is best to use coarse salt or special aquarium salt. Do not use seasoned salt containing additives, such as iodized salt. The salt should be dissolved in advance and roughly filtered before being added. The salt concentration should be gradually increased over 1-2 days to avoid causing osmotic pressure fluctuations in the fish.

The salt concentration must reach 0.3%-0.5% to achieve the effect of regulating osmotic pressure. This concentration is very safe for the vast majority of fish. Some fish, such as some "soft water" fish and some catfish, are very sensitive to sodium chloride, so salt must be used carefully. In addition, excessive salt use can cause excessive osmotic pressure, which will further lead to physiological changes in body cells and reduce the fish's ability to resist disease. When the salt concentration exceeds 1%, even short-term soaking can cause adverse reactions in fish.

Conclusion

For many early-stage fish diseases, the combined use of the "Old Three" will produce very good results. Personally, I think changing the water is the core, and rapidly reducing the content of bacteria and viruses is the foundation of treatment. Changing the water can be used alone, while raising the temperature and adding salt should be used together. I hope this article can help more friends understand the treatment mechanism of the "Old Three" so that we can make better use of it. If there are any shortcomings, I hope the seniors can offer guidance.