Selecting your first fish

The aquarium has been cycled- water parameters are suitable. The next step is to run down to your local pet/fish store and buy some fish you like. Not so fast!  You sure your water parameters are correct for those fish?

A mistake was made by many, including myself, when I started my first aquarium. So eager to get my first freshwater fish home, only to be disappointed and wondering why some died so quickly.

Thanks to the wonderful Worldwide Web, it has ample information about aquarium fish species to make sure the species you select will thrive in your water parameters and with other species you’ve chosen for your first aquarium.

First, we’ll examine water parameters, then move on, making sure the species you’ve selected will enjoy each other’s company.

Selecting Fish
Fish in an Aquarium

Water Parameters

Water parameters are essential when selecting fish for your aquarium, with pH, temperature, and hardness being the highest on my list.

Say you want Angelfish in your aquarium – a simple online search for “Angelfish water parameters” will summarize the fish tolerances for pH, water temperature, hardness, and possibly breeding and compatible species information.

Let’s examine each of these parameters.

  • pH – the reading for how acidic or basic a solution is using a scale from 1 to 14 where 7 is neutral. The lower a pH reading goes, the more acidic the solution becomes.

Conversely, the higher a reading goes, the more alkaline the solution becomes. What does this mean for aquarium fish?

In the wild, fish are accustomed to certain pH levels, with slight variations from time to time. Their “wild” cousins and most aquarium-raised fish also adjust to fluctuations in pH levels, but why would you want your fish to live in conditions different from their natural habitat?

You don’t! They will be happiest “thriving” in waters similar to their origins.  Just like we need air, fish need a proper pH level.

pH Chart
pH Chart
  • Temperature – is crucial to keep a healthy fish and could create an environment to induce spawning as long as other parameters and habitat are met, just like humans, where one person is comfortable at 72 degrees while someone else might feel cold.

Fish are happiest when their water is within the ideal temperature range (e.g., Angelfish prefer water at 78-84 degrees Fahrenheit). Moving fish from one temperature to another without giving the fish a chance to acclimate to the change can often result in the fish dying.

  • Water Hardness – also known as hard or soft water, has a vital correlation to pH. Hard water that is higher in minerals act as a buffer making it harder to lower the ph.

Higher pH correlates with hard water, whereas soft water is a lower pH is likely. Different species require different water hardness (i.e., soft versus hard).

An easy way to determine if you have hard water is to look at your shower head. If there is calcium buildup on the head, your water is probably hard. Hard water leaves those pesky water spots on your dishes as well. If you are unsure, you can purchase a water hardness test.

  • Ammonia, Nitrate, and Nitrite – levels will need to be monitored as well, but as long as you cycle your tank and regularly check the levels, they should not affect your selection of fish.

A simple online search on these and other water parameters before you purchase fish online at a site or from your local fish store will ensure a successful purchase and that your fish will have the best chance of living a healthy, long, and happy life!

Selecting Your Fish

What do you need to look for when selecting fish that can live happily together? It’s important to remember that not all species are compatible.  Here we will cover water parameters, fish aggressiveness, and space needs.

Piranha- Most aggressive Aquarium Fish
Piranha- Most Aggressive Aquarium Fish
  • Water parameters – probably the easiest way to narrow your search after making an initial selection of fish. Make sure the water parameters required by each species are similar.

The temperature will likely be the deciding factor, but pH tolerances, water hardness, and other parameters should be considered. Most domestically bred and aquarium-raised fish can handle a wide range of temperatures, but, again, why not provide the best conditions for your fish.

Selecting fish at random increases the likelihood of choosing species requiring different water parameters resulting in some species not surviving. Look for species with similar water parameter tolerances (temp, pH, water hardness), which will lead to happy, healthy fish.

  • Fish Aggressiveness – as mentioned earlier, not all fish species are compatible. Some are more aggressive.

Having aggressive fish with more “community-minded” fish is not normally recommended. Aggressive fish not placed with compatible fish can become aggressive, territorial, or fighting for food and/or mating.

It would be best to be cautious when placing aggressive fish with a smaller species who the larger, more aggressive species will constantly terrorize. Online searches are very useful in determining the aggressiveness of different species.

  • “School Size” – You also want to look at the species’ preferred “school” size, whether it is two fish or ten fish needed for them to be happy.
School of Fish
A School of Fish
  • Water Depth Preference – fish like to be in a specific depth range within an aquarium (i.e., bottom, mid-range, or top). If you want more fish in your tank, research their ideal tank range and select species that inhabit different depth ranges.

Some species live on the bottom (plecostomus) of the tank and may feel safer when other compatible species are swimming above them. In the wild, fish use other fish to alert them of predators. Fish in your aquarium also have those same survival instincts.


While we haven’t addressed all parameters or information needed for selecting fish for your new aquarium, keeping these few in mind will increase the likelihood of establishing an aquarium with healthy and happy fish!