Fish compatibility and selection is something you should take a lot of time considering before you even plan begin to cycle the tank. If you haven’t then you definitely have a lot of homework to do before you add fish to the aquarium. Avoid impulse fish buys and don’t take the word of a well intentioned but often incorrect fish store staff. Research all the fish you want from multiple sources and plan your aquarium ahead of time. This is how you can minimize fish loss when you stock your tank and this is the fastest way to having a stable and successful aquarium.
⇐Freshwater Fish Saltwater Fish⇒
Aggressiveness and Fish Compatibility and Selection
Aggressiveness and fish compatibility follow the same rules for both saltwater and freshwater aquariums. Typically fish can be split up into passive, semi-aggressive, and aggressive. The fish that are considered passive do not typically eat other grown fish and will do well with pretty much any other tank mates that won’t harass or kill them. They are often schooling type fish but can also be solitary and peaceful. These are the types of fish you will want for community aquariums and most planted aquariums as well. Most of the more aggressive freshwater fish will tend to uproot, eat, or otherwise destroy plants. A more aggressive coral tank is possible though.
Semi-aggressive fish are usually a little bigger and can be passive or aggressive depending on their tank mates. They often engage in territorial posturing and can harass more passive and smaller fish, even to death. If you mix semi-aggressive with passive fish there might be an increased chance of ich in the aquarium due to the passive fish being stressed out and the loss of some of the weaker fish is likely. Sometimes, you can add a smaller semi-aggressive fish to an established community tank when it is young and it will grow up to be a part of the community. It is important to monitor the behaviors of the fish in the tank to see if there is any major change in fish compatibility. A fish that is too dominant and harassing other fish can sometimes be better off being traded in or given away. Sex is also an important factor in compatibility when dealing with more aggressive fish. Too many aggressive males will can create a hyper aggressive tank. Most semi aggressive and aggressive fish will be much better off with a higher female to male ratio … around 2 to 1 or sometimes it is best to just keep them as a solitary species. The sex ratio doesn’t seem to matter much with more passive and schooling fish.
Fish that are classified as aggressive are typically predatory fish that will literally eat pretty much anything it can fit in it’s mouth. They can usually only be kept with other aggressive and suitable semi-aggressive fish. The more aggressive the fish get the more and more size will come into importance and consideration. This is because a small passive fish is compatible with a large passive fish and a smaller aggressive fish might be ok with larger passive fish but larger aggressive fish will most certainly kill smaller and less aggressive fish. Having a large predatory fish aquarium is certainly a huge thrill and a pinnacle of aquarium keeping. However, be prepared for the extra time and expense involved in setting up and maintaining such a system. Ultimately, a small countertop aquarium can give one just as big in satisfaction and thrills.
⇐Freshwater Fish Saltwater Fish⇒
Aquarium Fish Bioload
Bioload is a term that refers to the amount of life existing in an aquarium and specifically the waste they produce. Some organisms such as plants or animals that are efficient eaters and grow rapidly may even have a net negative effect on bioload.
Every animal in your tank produces waste in the form of solid or liquid excretions. This waste consumes oxygen as micro-organisms eat it and break it down into its basic nitrogen components.
Every piece of food you add to the tank which is eaten by your animals, contributes to this waste as does any piece which is not eaten but lies in a forgotten corner of the tank and this becomes food for bacteria and other microorganisms.
This amount of waste being made is really the ‘bioload’. In a tank the most obvious signs of a bioload observed and measured are the ammonia, nitrite and nitrate levels. Aerobic bacteria reduce the ammonia and nitrite to nitrates. Nitrates are removed with water changes and/or denitrification with a specialized denitrator nitrate removal filter.
However, the bioload is never constant, as your animals grow you need to add more food to feed them and so they will produce more waste. If your filter is not working well (perhaps due to blockage) or is undersized to cope with the free toxins, this often allows algae and other excess bacteria to grow outside the filter therefore consuming more oxygen. So the bioload of your tank can increase over time.
Planning for Proper Bioload
It is important to plan your bioload ahead of time so that you are fully prepared for the maintenance of the aquarium. This will ensure success of the tank and reduce the risk of tank crashed, fish disease, and other common aquarium problems.
An old rule of thumb is 1″ of fish per gallon of tank. This is true for smaller and midsize or leaner fish. For larger and bulkier fish we would recommend being more conservative and only recommend 1 inch of fish per two gallons of tank. This is because a bulkier fish such as an Oscar or a Goldfish will have a higher metabolism and bioload when compared to a thinner fish. You also want to use the fish at their full grown size and NOT the size you buy them (unless you plan on getting a larger aquarium as they get larger.)
Let us provide some examples. In a 10 gallon tank, 10 small neon tetras that will only be about 1″ when fully grown is an appropriate bioload. If you instead get the larger, bulkier black skirt tetras that get up to 2″ in size, 5 fish will be a more appropriate fish load.
In a 55 gallon tank you could put up to about 55 small tetras. However, most people will keep a variety of fish in a 55 gallon aquarium. Discus are fish that are fairly bulky and get up to 8 inches but can also be kept with schooling tetras. You could keep up to 3 and a half discus comfortably in a 55 gallon tank. We will divide 55 by two inches and arrive at about 28 inches of larger fish. Each discus can get up to about 8 inches so 28 divided by 8 is 3.5. Of course, you will not be keeping a half of a fish. If you have 4 discus in a 55 gallon tank you will want to be more aware of water quality when they become full grown and do water changes more frequently or use a quality nitrate filter. Aquarium plants will also assist in maintaining the water quality. You could also get 3 discus and then also have 8 small tetras or other small community fish.
The same rule would apply to goldfish, about 3.5 goldfish is appropriate for a 55 gallon aquarium. Goldfish also are bulky fish that get up to about 8 inches. So three goldfish and a pleco (which is a bottom feeder and so has less of an impact on bioload) is an appropriate bioload for a 55 gallon aquarium. This is far less than many people will have in mind when they set up an aquarium but we assure you this is optimal.
Cichlids can vary in size and girth significantly with Oscar cichlids being extremely bulky. A thinner cichlid that reaches only 5 inches such as the Electric yellow cichlid is very different from a fat Oscar than can get up to 12 inches. In a 55 gallon tank, you could keep up to 11 or 12 smaller cichlids but 8-10 would likely be easier to maintain. However, 2 Oscars max would be appropriate for a 55 gallon tank and really they are so bulky and big they would be better off in a 65-70 gallon tank.
Saltwater fish will follow the same rule of thumb but many saltwater fish are more sensitive to water quality and if you have corals they will also be more sensitive to water quality. This is why a slightly more conservative bioload is usually found in most saltwater aquariums.
You can have a bioload up to about 50% greater than recommended but be aware that you will definitely need to spend more time maintaining the system and replace the filtration more often. As you increase the bioload the chances for fish disease, tank crashes, and other issues such as cloudy water will increase. If you attempt a bioload higher than 50% over the recommended level you will be inviting trouble and you will likely find yourself in over your head and a tank crash or serious issues will at some point become almost inevitable.
The Aquaripure Nitrate Removal Denitrator filter operates at it’s best with an optimal bioload. It will make is easier to have a slightly heavier bioload than recommended but you will still be maintaining the denitrator and the tank more than with the optimal bioload. At bioload levels more than 50% over the ideal you will likely find nitrate levels an issue regardless of water changes or denitrification.
Every aquarium ecosystem can have endless variables. However, it is important to give your aquarium the proper forethought and planning and to thoroughly understand the principals behind the nitrogen cycle, aquarium filtration, water changes and/or denitrification and proper bioload planning in order to make sure you have a successful aquarium ecosystem that you are able to sustain and maintain.
Recognizing and Handling High Bioload
One sign of a high bioload is that the level of oxygen in the water is too low to adequately support active animals in the tank. The animals keep near to the surface (if they can) and in the small hours of the night, the animals may be scrambling for air at the surface. But the owner all too often never sees this regular night time warning. This can also be a sign of poor water circulation and oxygenation. This can be even more pronounced in a planted tank at night as aquatic plants will also absorb oxygen at night (in the day they produce oxygen and absorb carbon dioxide.)
Other signs are algae blooms, cloudy water, ammonia in the water, and brown bacteria that appear on surfaces throughout the tank as the bacteria population climbs to take advantage of the excess organics in the system.
If your tank has a high bioload then extra filtration is in order. You will need to change and clean the filters more often. A little more biofiltration will help with any ammonia spikes. Use of activated carbon will help keep unwanted trace elements and organics from building up. In a saltwater aquarium, a skimmer will help if you do not have one. In a freshwater aquarium, plants and invertebrates or more bottom feeders can help. A UV sterilizer might be necessary to combat algae and cloudy water issues. You will also need to do significantly greater water changes and/or utilize a Nitrate Removal Denitrator Filter. Requirements of a 50-100% weekly water change or even more is not uncommon in a tank with a heavy bioload. The Aquaripure Nitrate Removal Denitrator filter will typically be the equal of up to a 50% weekly water change.
In some extreme case, you will be doing both yourself and your fish a huge favor if you find a better home for them by either giving them back to a fish store, another aquarist, or investing in a larger aquarium system. If you really want an easy to care for tank, a fairly light bioload and a good filtration system including an Aquaripure Nitrate filter will give you years of enjoyment with a minimum of upkeep and effort.
Sponsored by Aquaripure, The Next Generation in Aquarium Filtration TM.
The Aquaripure filter is a comprehensive biological filter which will completely process all organic matter and remove all nitrates in an Aquarium. These filters are known as a nitrate filter, nitrate reactor, denitrator, biodenitrator or nitrate removal filter. Other biological filters only convert organic matter into nitrates which then accumulate in the aquarium, physical filters only remove larger particulate matter, and skimmers do not remove any nitrates. The Aquaripure uses beneficial bacteria to break down invisible organic matter and nitrates completely into Nitrogen gas which then escapes into the atmosphere. This same process is even used by some water treatment plants to make wastewater safe for human consumption and to clean polluted water. The Aquaripure does this in an extremely safe and controlled environment and after the water from the Aquaripure is aerated there is nothing left but pure, clean, crystal clear water.