Fish Tank Chemistry 101: Freshwater Aquarium pH

Freshwater fish tank PH

Fishes don’t actually live in waters that are too static, inert or free of anything but just pure water itself; they live in environments that having changing levels of acidity and alkalinity, often known as the pH levels of water.

Now, don’t get confused: although it is termed as acidic, it’s not your stereotypical green oozing liquid that melts anything that it touches.

Acidic in chemistry terms is just the rate of how high is the concentration of hydrogen ions (H+) in a solution after being dissolved in water, which is basically the exact opposite of alkalinity which is determined by the number of hydroxide atoms (OH-).

pH levels in a Fish Tank

Water pH is the general measurement unit for testing the acidity or alkalinity of water. For acidity, anything that is less than 7.0pH is considered as acidic, while anything greater than 7.0pH would be considered alkaline. It is important to know the exact measurements of your fish tank water’s pH and to research about your fish’ pH level tolerance. Neglect of these important variables can potentially cause your fish’s early death.

Measuring pH levels

There are a number of available pH level test kits out there in the market, although it’s still up to the hobbyist on how to use the testing kit properly. Some hobbyists have the tendency to use the pH test kits on tap water right away, without considering the fact that the pH levels of that tap water can change considerably upon use as water in your fish tank. So, you have to test first the water by putting some rocks and gravel into it, and leaving it for about 24-48 hours (leaving the water for a week before testing  works best, although it is indeed a bit time consuming). Then, test the pH levels afterwards, and see if there is any significant change in the water.

Consistency is the Key

For fish, it is vital that you keep the pH levels at a constant rate. They are most likely to get stressed by changing pH levels (for example, a water pH level that constantly shifts from 6.6 to 7.0) even if it’s suitable for the fish’s pH tolerance levels.

This doesn’t mean that you should get it at and exact constant rate, though that would be very difficult. Just keep it at a very low pH swing rate, something at around 0.2 unit change in pH levels should already be tolerable enough for your fish.

Changing the Water pH levels

Usually, the dissolved minerals in the rocks and gravel that you use in your substrate would already provide the right pH that you need for your aquarium, but there are other several methods to manually manipulate your freshwater aquarium pH levels.

Water has a property that is called the buffering capacity, which is the ability to resist any change in pH levels. You should take note of this very well, because even if you put additives in the water to change its pH levels, you might end up as if you did not put the additive at all, because of the high buffering capacity of the water that you are using.

The most common method to increase the water pH levels is to add crushed coral to your substrate. The coral’s composition reacts to the water, and subsequently raises the water’s pH level and maintains it at a certain rate.

Remember that pH levels constantly drop over time, so changing the water periodically is necessary to maintain the pH levels at a constant rate. Alternatively, there are available buffers in the market that can raise the pH levels of your fish tank, but beware of using them in large amounts unintentionally.

If you want to lower your freshwater aquarium pH levels however, then there are also several steps and measures to do so. One is to increase the carbon dioxide levels of the water.

Don’t add too much, just enough for the pH levels to tip off and go over the lower pH zone. Synthetic Chemicals that lower pH levels are also available, but like always, you should be wary of the amount that you are administering in your fish tank.

What are the Best Fish For your Freshwater Aquarium

Setting up your first freshwater tank is both rewarding and challenging. This is especially the case if you choose fish which are more difficult to keep healthy.

Thankfully, there are a number of adaptable, hardy fish for your freshwater fish tank which are inexpensive. It’s not too difficult to find good fish for your first tank.


Guppies are a logical first choice if you’ve never kept fish before. You can often buy these fish as feeder fish – you can buy them for as little as ten to a dollar. Until they grow up, they’re not much to look at, but they make for a great starter fish.

These feeder guppies can actually be very attractive once grown. If you don’t have that kind of patience, you can also buy adult guppies for your tank.

Guppies get along well with other fish and are easy to care for. Guppies are so adaptable and hardy that you shouldn’t be surprised to find them reproducing in your tank!


If you’re not so crazy about guppies, tetras are also a good choice. Tetras are smaller and by themselves, not so impressive.

However, they are happiest in groups; consider getting a school of them for your tank. These fish also tend to get along well with others and rarely cause trouble in a tank.


Gouramis are a good choice if you prefer larger fish. Since the males tend to be aggressive towards each other, a pair is probably the best way to go with Gouramis.

They are also easy to take care of and rarely attack other types of fish.


Loaches are also easy fish to care for and mix well with other fish. Except for the more loner-type yoyo loach, loaches like to have other loaches around. They’ll need a place to hide during the day, so give them rocks or pipes.


Barbs are easy to take care of and good in schools (you’ll want at least four). However, they do not mix well with guppies, angelfish or other long-finned species, since they can shred their fins.


Angelfish are popular but can be problematic. They are often bullies and will eat smaller fish like guppies and tetras). Furthermore, any fish larger than them will tend to damage their fins! If you really want angelfish, it’s best to have them in their own dedicated tank – they prefer to have at least one other angelfish around.

Freshwater Fish Tips: 10 Things Not to Do

freshwater fish dos and don'ts

Do not buy a new tank and fish at the same time

One of the most important parts of setting up a new freshwater aquarium is ’cycling’ the tank.

Once the tank is decorated, the water has been added and the equipment is operating, you have to allow the tank time to build up good bacteria.

This process can take weeks depending upon the size of your tank. Check the tank water every couple of days to be sure that the cycling process is complete before adding fish.

Change more than 20% of the water at one time

If you change too much water you will upset the balance in the tank. You will be killing off the good bacteria.

If you add less than 20% you do not have to treat the water for chlorine and chloamine but if you add more than 20% you should be treating the water. If the two water temperatures ( the tank and the new water) are not the same you may shock the fish.

Do not put too many fish in your tank

Over crowded fish are prone to stress and disease. Your fish need room to swim and grow.

They also need oxygen and if there are too many fish in the tank there may be an insufficient amount of oxygen.

Do not over clean

It is not necessary to clean everything in the fish tank at one time. By doing this you are actually killing off the good bacteria.

Clean only a piece at a time if you are having a lot of algae build up. Give the tank time to adjust before you clean another plant or ornament.

Do not use chemicals

No matter how many times you rinse something you can never be certain that you have gotten off all the toxins.

To avoid a potential disaster do not use any chemicals or soaps to clean anything. When washing or cleaning the filter or decorations it is best to rinse them using old fish water.

This sounds as though you are not really cleaning, but remember you only want to rinse things and you are trying not to upset the tank balance.

Do not over feed

Fish will over eat and they will get fat. This condition is just as unhealthy for fish as it is to humans.

Do not buy more than 3 or 4 fish at a time

Even if your tank has been up and operating for a long time you do not want to bring home more than 3 or 4 fish at a time.

You still need to give the tank time to balance itself out before adding more new residents. This also gives you time to be certain that there is not going to problems caused by the new additions.

These problems might include a lack of oxygen in the tank or a water imbalance. You also will have time to make sure that the new fish do not have any diseases or infections before adding more fish.

Do not depend solely on scavengers

While scavengers do help to keep both the gravel and the glass clean you are still going to have to help them. The gravel will still need to be cleaned and the glass will need to be scraped.

How to Setup a Freshwater Aquarium: A Beginners Guide to Fish Tanks

Owning your own aquarium is great fun, and I have been maintaining my own with love for many years! There’s over 60 million of us aquarists worldwide, and if this is a hobby you’re interested in, its worth a little time to learn what its all about before you start.

So whats an aquarium?

In the simplest terms, its a transparent container where you can keep, nurture, observe and enjoy live fish.

The goldfish bowl with a single fish in it counts, but what most people mean when they talk about aquariums is a large fish tank (usually rectangular) with several different types of fish and aquatic plants living in balance with each other.

There are two basic types of aquarium environment freshwater and saltwater.

Freshwater aquariums are definitely easier for people who are new to the hobby, as the saltwater (or marine) tanks take a great deal of attention and skill to keep the fish alive. So your next step is probably to find out what types of fish you like.

If you’re lucky, you have fishy friends you can ask questions of, but even a trip to your local pet store or specialty fish store will get you lots of good advice from the sales clerks.Tell them youre a beginner, and that you want to look at freshwater fish, and they will give you lots of choices!

  1. Finding the one fish that calls out to you will tell you what temperature your tank needs to be, and starting with one species is probably simplest.
  2. Next, I’d get a good book about basic aquarium care, and read it before you get started!
  3. Then, start collecting your tank and equipment. You’ll want to look for a sturdy aquarium that’s big enough to give you room to add fish as your experience grows. Practical home fish tanks range from about 11 liters (3 U.S. gallons) up to about one cubic meter (300 U.S. gallons) in size.
  4. You’ll need gravel, or another substrate, for the bottom of the tank.
  5. You’ll need a filtration system, to remove waste and phosphates from the water, and a heater or cooler mechanism to keep the water temperature right.
  6. You may need an air pump to oxygenate the water, depending on your tank setup. Also ask about a small chemical kit for measuring and correcting the pH balance in the water.
  7. You’ll want to investigate the plants, rocks, and other aquarium furniture that goes into the tank.

Choose carefully, because the wrong materials can be harmful or even poisonous to your fish!

Get your tank set up, and make sure that the water temperature and pH balance is correct BEFORE you go back to the store to get your fish! If you’ve done everything correctly, your fish will be healthy and happy, and you’ll have a fascinating new hobby to learn and love!

Selecting an Aquarium

There are hundreds of models of aquariums on the market. Not only do they come in all shapes and sizes, but many places offer tanks as large show pieces of furniture. You can get anything from a coffee table aquarium to one that is custom made to fit in your wall.


What kind of fish do you want to own?

A good example is if you want to own an oscar. An adult oscar can grow to be 12 inches. The size of the fish should be taken into account when selecting your tank.

You should also take into account how many fish you want to have. Never over crowd your aquarium, not only is it unfair to the fish, but you will probably end up with a lot of trouble with your ammonia and nitrite levels.


You are going to have to decide how much you want to spend on your new aquarium. When planning out a budget consider the equipment that you will need and the price of fish. There will also be a small ongoing monetary commitment to both food and replacement parts.


Before bringing an aquarium home, carefully figure out exactly where the tank is going to be set up. Ensure that you have a proper stand that will support the weight of the tank and be sure that it is not in direct sunlight or drafty areas.

Glass or Acrylic

Glass can crack, chip or break, however, it does not scratch as easily as acrylic.

Systemised Tank

These tanks usually come with both the heater and filter system built right in. If you are looking at purchasing one of these tanks, be sure to find out where you can get replacement parts and accessories that might be required. Systemised tanks are great for beginning tank owners because basically all you have to do to set them up is add water, cycle and add fish.

Aquarium Kits

These are great for beginning tank owners. Most kits usually have both a heater and a filter which are the right size for your tank. They usually contain a few other small pieces of equipment. It is important to take a good look at the contents of the kit, as there may be a few things that you need which are not included.

Bare or Basic Tank

You can purchase just the tank and usually a canopy. Buying this way offers you more choice in what kind of equipment you purchase and how much you spend, allowing you more control as a customer. The type of filter and heater is not pre-selected so be careful with your choice, make sure that they will do the job correctly. You do not want to buy a filter that is either undersized or really oversized for your tank. By purchasing a tank this way there is not going to be any unwanted or unneeded equipment. For instance, you might not need a heater if you are planning to keep a fish that prefers colder water temperatures.