We will be going over the most important thing in fish keeping, the nitrogen cycle, and why it is important to perform water change.

“The filtration cycle must be complete before putting fish into the tank. Usually the cycle takes a couple weeks but there are a lot of products on the market that helps speed the process along.”

Nitrogen Cycle? What is that?

Two types of pollutants can arise after feeding: fish excrement and leftover food. The fish eat most of the food but small crumbs can float in the water, rot and contaminate the water. The contaminants turn into ammonia and stay in the water. This is a problem because ammonia is very detrimental to fish.  Therefore, we need to create an environment that beneficial bacterias that break down ammonia can live. This procedure is called The Nitrogen Cycle. If you put fish in a tank that is devoid of this beneficial bacteria, the ammonia amount increases and within a couple of days, the fish die. 

Most beneficial bacteria live everywhere in the tank: on the walls, the substrate, driftwood, etc. However, the best place that the bacteria can live, and the area where there is the most bacteria, is the filter. So some fish keepers that already have a cycled tank, install a second new filter and after one to two months, once a lot of bacteria is living in the filter, move it to a new tank to successfully cycle it. 

In a tank that is cycled, the bacteria eat ammonia and convert it into a less poisonous substance called nitrate. Even nitrate, in large quantities, is poisonous to the fish so water change is used to get rid of build up of nitrogen and refill it with clean water.

How to perform a water change?

Now that we learned why we have to perform water change, we will now go over how to successfully execute water change. There are a couple things to be cautious of when performing water changes. 

First, it is not good to change a large volume of water at once. There are various substrates in the water and chemical reactions happening that affect the fish. Except for certain special circumstances, If you change more than 50% of the water in a tank, there will be a sudden and significant change which can have a negative effect on the aquatic animals. 

Second, it is best practice to know the exact condition of the water before changing. There are a lot of different water test kits on the market. I recommend API water tester. It is best to test the water frequently and perform water change accordingly. 

Third, in a way, it is connected to the first point. Many fish keepers say that the fish are acting weird after a water change. I believe that most of the problems arise because the new water was not the same temperature as the original tank water. Aquatic animals are generally sensitive to water temperature, so if the original tank temperature was 70 degrees and the new water is 40 degrees, the water temperature would suddenly drop to around 55 degrees. In that case, fish can contract flu like symptoms and it can spread to the other live animals in the tank. In serious cases, a fish can faint. Therefore, it is crucial to match the temperature of the new water to the original water before changing. It would be convenient to have a thermometer right? 

Fourth, frequency of water change can differ by situations. It can differ based on what kind of feed, how much feed, how many fish in the tank, etc. Feeding frozen feed or live feed, such as shrimp and worms, can pollute the water quicker because the feces contain more contaminants. 

Fifth, if the tank has live plants, you can get away with less frequent water changes. Aquatic plants basically grow by consuming substances in the water. They can also consume ammonia or nitrogen like matter. This would cause a better environment for the fish, yes? However, this effect is insufficient to depend on so you can not drop water change altogether. Sometimes, you can see some fishkeepers with a tank with a lot of water plants to minimize water changes.

Finally, I will give you an example so it is easy to understand. The environment and situation can be different so rather than copying, please use it as a guide.

I have a 27 gallon tank that house 10 guppy fish and 2 pleco. I feed dry food twice a day. In this environment, I perform a 30% water change every 2 weeks.

If I change the food to worms, then I would perform 30% water change every 1 week.

Now, the guppy fish laid eggs and there are 30 guppy fish in total. In this case, I would perform biweekly water change. Similarly, you need to adjust the water change frequency based on the current condition. Ofcourse, you should check the water parameter with the test kit after each water change and make sure it is at the right level of water quality. If you use the water test kit and the contamination level is high, it would be best to perform water change more often or increase the amount.