Fish Causing Problems in Planted Tanks

Fish Causing Problems in Planted Tanks

Keeping a planted tank is a dream of many hobbyists. However, it can also be very challenging because you have to know such things as: lighting requirements; the chemistry within the water that allows the plants to thrive, and compatibility plants with fish.

When we choose fish for the planted tank, we often come up with the question of which fish are safe to keep with plants. What kind of damage we can expect? Will the fish completely destroy the plants or they will only nibble on them from time to time? What fish species do we need to avoid in planted tanks at all?

Keep on reading for everything you need to know about fish and plant compatibility, including background information with practical and proven tips to reduce the chances of turning your beautiful planted tank into total chaos and destruction.

Fish and Plant Problems

The question of the compatibility of aquarium plants with some species of fish is very debatable. On the Internet, you may often come across completely contradictory results.

Whereas some people complain that these or that fish species are incompatible with aquatic plants, others will tell you that they have never had any problems with them.

Why and how is it possible? Why the same fish species in one tank are exemplary tenants and in others, they turn into Hulk mode? How do some aquarists manage to keep plant-eating fish in their planted tanks?

Personally, I can see several factors that play a huge role here.

  1. Natural feeding preferences.
  2. Hunger.
  3. Fish behavior.
  4. Plant species.
  5. Water requirements

Let me give you a short explanation.

1. Natural feeding preferences

All fish species can be divided into three categories:

  • Carnivores
  • Herbivores
  • Omnivores 

Carnivorous fish species favor a meat-based diet, therefore, they will not eat your plants. For example, these are Oscar, Goliath tiger fish, Vampire tetra, Killifish, Snakehead fish, Peacock bass, Giant wolf fish, Alligator gar, Discus, Arowana, Pea Puffer, Piranhas, etc.

Herbivorous fish species mostly prefer algae, fruits, seeds, and plant matter. Nonetheless, it does not mean that their diet is completely vegetarian. They can and will eat small animals as supplementary food if given a choice. For example, Pacus, Silver Dollars, Farowellas, and Mollies are primarily vegetarian fishes.

Note: It is interesting to know that, herbivorous fish have a pretty small stomach, meaning that they need to eat frequently. Obviously, that is not good for planted tanks.

Omnivores fish can eat a variety of meat and vegetable matter. They do not have strict preferences because their stomachs usually possess some of the traits of both the carnivore and the herbivore.
Note: The majority of fish species are omnivores.

2. Hunger

Will fish eat plants in the tank also depends on how hungry they are. Some herbivorous and omnivorous fish have high chances to turn against plants when they are hungry.

To be honest, in this case, you can blame only yourself. They are following their instinct of survival that forces them to eat anything they can find.

Therefore, keep your fish well-fed, especially in a tank with expensive and rare plants. Do not tempt them to taste the plants.

3. Fish Behavior

Piranhas bite plant
Jorge Silva – Associated Press

Fish behavior can also be a huge problem for planted tanks. For example, if the fish is a carnivore, it does not exclude the fact that some of these species can simply break, or uproot the plant because they are nest-builders.

Do your research, for example, you can choose plants that do not require substrate at all. Another way of preventing fish from digging is to place big stones around the plants.

4. Plant Species

Another problem is that many of the plant species have very thin and fragile leaves. Therefore, it does not take much for the fish to nibble, eat or simply tear them up.

Therefore, we have to take into consideration the fact that big and strong fish can completely destroy the plant without even eating it.

5. Water Requirements

In some cases, it can be close to impossible to keep certain species of fish in planted tanks because of specific water requirements (PH, GH, and KH) that plants need.

For example, in order to add African cichlids to planted tanks we need to understand that majority of aquatic plants prefer to live in a neutral pH and low KH, and GH. While African cichlids need a pH of 8.0, GH and KH should be between 10 and 20. So, if we put sensitive plants in such water it can kill them.

Tips on Feeding Herbivorous and Omnivorous Fish

Unfortunately, if you have plan-eating fish, there are no ways to absolutely prevent them from doing it. It is simply not impossible to guarantee that they will not touch the plants.

However, you can reduce the chances of turning your planted tank into a wasteland by feeding a lot of vegetables (lettuce, cucumber, zucchini, broccoli, lettuce, etc.).

Although some people feed it raw, in my experience, blanching works best for every fish involved. It is safer, easier, and tastier for the fish to eat.

You can read more about it in my article “How to Blanch Сucumbers and Zucchini for Shrimp, Snails and Fish the Right Way”.

Fish That Can Cause Problems in Planted Tanks

It is not possible to name all fish species that potentially might create problems for the planted tanks. Therefore, I will name the most popular ‘offenders’ you need to keep your eyes on.

  1. Goldfish (Carassius auratus)
  2. Buenos Aires Tetras (Hyphessobrycon anisitsi)
  3. Silver Dollars (Metynnis argenteus)
  4. Oscars (Astronotus ocellatus)
  5. Mbuna
  6. Siamese Algae Eaters (Crossocheilus siamensis)
  7. Mollies

Some ‘Honorable’ Mentions.

1. Goldfish 

Goldfish (Carassius auratus)There are over 125 goldfish varieties available today. The properly cared for goldfish can live as long as 15 plus years. In addition, this is not a small fish, depending on what species of goldfish that you are keeping they can get over 12 inches (30 cm) long.

  • While goldfish are technically omnivores, they are really primarily herbivores and eat plants with pleasure.
  • In spite of their size, these fish do not have big stomachs and their digestive system is built around grazing all day. It means that it would be better to feed them very small amounts of food 2 – 3 times a day, instead of one big feeding.
  • Goldfish often sift through the substrate that will be a problem for rooted plants.

Goldfish can be potentially distracted by Duckweed. They love this plant so much that they will prefer it over any other plant. Hard plants like Anubias, Java Fern, Cabomba, Amazon Sword, Hornwort, Brazilian Pennywort, Ludwigia, Rotala, Lysimachia nummularia, etc. have more chances of survival in the tank with goldfish.

Note: Keep in mind that the size of the tank also affects their behavior. In small tanks, big fish get bored very easily, so they can start destroying the plants.  A common guideline many keepers use is a minimum of 20 gallons (80 liters) of water for the first fish and 10 gallons (40 liters) for each additional fish and even that is too small for full-grown goldfish.

Related article:

2. Buenos Aires Tetras (Hyphessobrycon anisitsi)

Buenos Aires Tetras (Hyphessobrycon anisitsi)Do not be confused by the name “Tetra”. Although in most cases, this is synonymous with small, peaceful, and community fish, this does not apply to all tetra species. Buenos Aires Tetras are small (about 2.5 inches or 7 cm) schooling fish that will also nip at their long-finned companions (Swordtails, Guppies, Angelfish, Betta, etc.).

They are one of the hardiest of the commonly available tropical fish, they are great for beginners that do not have plants in the tank. In planted tanks, they can become your worst nightmare.

  • Buenos Aires Tetras are In the aquarium, they will generally eat all kinds of foods including plants. Plastic plants are the best choice with this fish. Do not underestimate the threat, you will regret it.

Only really hard plants like Java fern have some chances with these fish. Even if you have to keep them well-fed all the time with blanched vegetables, it may not be enough to distract them from live plants.

They are extremely active fish and eat like they have not seen food in days. Other all, Buenos Aires Tetras are not a good choice for a community tank or a planted tank. 

3. Silver Dollars (Metynnis spp.)

Silver Dollars (Metynnis argenteus)Silver Dollar fish are native to the Amazon River. The average Silver Dollar fish can reach almost 6 inches (15 cm) in length and live for 10 years or more in captivity. They should be kept in a school of 4 – 6 individuals, which means a large tank (at least 50-gallon or 200 liters).

They are very common in pet stores and can be kept from beginner to expert level aquarium hobbyists.

  • Unlike their distant carnivore cousins – the piranha, they are omnivores with a huge appetite for live plants and vegetables. That is why they are often called “Plant piranhas”, however, they are not exclusively vegetarian.
  • Generally, Silver Dollar fish are peaceful but can be extremely aggressive eaters.
  • These fish are very sensitive to light, they simply prefer to stay in the dark, which can be a problem for the planted tanks.
  • They are also active and fast swimmers meaning that these fish require a lot of open space in the tank. This is also not a good feature for the planted tanks.
  • Silver Dollar fish can uproot plants in the tank.

On the Internet, some guides on keeping Silver Dollar fish suggest using only very sturdy live plants like Java fern or Hornwort.

Well, I have done my research and also asked some friends of mine about it. My conclusion is – do not risk it. Sure, you might be lucky for some time but eventually, they eat everything.

Therefore, the only viable option for these fish is plastic plants or some cheap plants that you are ready to lose.

4. Oscars (Astronotus ocellatus)

Oscars (Astronotus ocellatus)Oscar is one of the most popular larger fish in the aquarium hobby. These fish do get quite big; they will get to 10 to 12 inches (25 – 30 cm) very easily and very fast. Therefore, they need at least a 75-gallon (~200 liters) tank.

  • Oscars will not eat the plants but they like to rearrange their tanks and constantly stir up the bottom. By doing so they will uproot any plants in your tank. Everything in the aquarium should be secured down. This is a very strong fish and can move even heavy objects.
  • Floating and sturdy plants might be safe for a while. However, Oscars are known for being moody and very clumsy. So, in one of these moments, they will simply tear apart any plants.

5. Mbunas

Psuedotropheus Demasoni Cichlid - Mbuna African Cichlid fish“Mbuna”, a word meaning “rock fish,” is used to describe a group of Haplochromines that are found on the rocky shores of Lake Malawi. These African cichlids are about 4 – 5 inches (10 – 13 cm).

  • These are the fish from hell for planted tanks. Generalist omnivores by nature, they are still closer to herbivores and tend to eat any aquarium plants if given the chance. Even though plants are not safe with this fish.

6. Siamese Algae Eaters (Crossocheilus siamensis)

Siamese Algae Eaters (Crossocheilus siamensis)Siamese algae eaters have an extremely useful ability that made them one of the longtime favorites in the aquarium hobby. They are great for eating beard and hair algae. Unfortunately, they do get pretty big (up to 6 inches or 15 cm) and require at least a 20-gallon (80 liters) tank.

  • Generally, these fish are considered as plant-safe. However, Siamese algae eaters seem to behave slightly differently when they are around mosses (Java moss, Christmas moss, etc.). It has been mostly reported by aquarists that they like to tear it up and feast on it.
  • In addition, there is a chance that Siamese algae eaters can start nibbling at some other plants if they cannot find any other food in the tank. Keeping them well-fed is the best way to protect your plants.

7. Mollies

Molly PoeciliaMolly fish are one of the most commonly kept fish amongst fish-keeping enthusiasts. There are more than 30 known species of Molly. A lot of people find these small fish (2 – 4 inches or 5 – 10 cm) very attractive because they have a lot of different color variants such as black, gold, red, white, green, blue, etc.

Molly fish are very hardy and can adapt to brackish and freshwater. They are also best kept in larger aquariums and a minimum size recommend is 20 gallons (80 liters).

  • They are technically omnivores fish meaning that they can eat all types of life frozen and artificial foods, however, they still prefer to eat algae and plant matter. Therefore, they are really primarily herbivores.
  • Mollies are ‘swimming stomachs’ and always hungry, they want to eat all the time and when they are very hungry, they are certainly capable of eating tender and soft plants like mosses, Duckweeds, Hygrophilia sp., etc.

Nonetheless, I would like to stress out that Mollies usually do not bother plants, unless they are very hungry for that. In addition, tougher plants such as Java Fern, Vals, Amazon Swords, etc. should be OK in any case.

Some ‘Honorable’ Mentions

  • Giant Gourami (Osphronemus goramy) – huge fish (up to 28 inches or 70 cm). They are omnivores and bubble nest builders. If they do not eat the plant, they will destroy it later.
  • Koi are likely to eat many varieties of plants in the ponds and the larger they are the more they will eat them.
  • Tinfoil Barbs (Barbonymus schwanenfeldii). They are often sold as beginner fish that are easy to keep and care for. The problem is that they get really big and better suited for ponds. Tinfoil Barbs can rapidly eat any plant even Amazon Sword, Vallisneria, Crinum, Java fern, etc. Note: Actually, it concerns most They eat plants. The larger, the hungrier.
  • Sailfin pleco (Pterygoplichthys gibbiceps) is another big fish that can eat any plant or simply break it through sheer weight.
  • Large cichlids should be avoided in planted tanks as well. They do enjoy digging or tearing up planted tanks.
  • Rainbow fish will rid your tank of Duckweed.
  • Dwarf Gourami. They usually do not eat plants but some aquarists complain that they constantly uproot plants and damage the roots of the floating plants. They can also tear apart plant leaves to add to their bubble nests.
  • Flagfish (Jordanella Floridae) have a tendency towards soft plants like Duckweed, Red root floaters, Water sprite.

In Conclusion

A fish may be the perfect starter pet, but not just any fish will do in planted tanks. There are many fish species in the aquarium hobby, some are more prone to eat or unintentionally damage plans (uprooting or breaking) than others.

That is why hobbyists that compulsively buy fish without proper research and put them in their planted tanks sometimes end up with no plants.

  1. It is important to understand the feeding preferences of the fish.
  2. Keep them well-fed.
  3. Omnivore and herbivore fish need a lot of algae or vegetable components in their diet. Supplement their diet with blanched vegetables.
  4. Do not overstock fish. It increases aggression and, in some cases, by eating plants in heavily planted tanks, they simply increase the needed space for them.
  5. Pick tough plans that can be hard to destroy like Anubias, Java Fern, Crinum Calamistratum.
  6. If the plant requires the substrate – protect it with stones, decorations, or driftwood, or they should be potted (if possible).
  7. Let your plants establish in the tank before adding any fish. These 2 – 4 weeks can greatly benefit your plants allowing them to root in and adjust to the enclosure.

All these factors play a huge role in determining the outcome of why everyone seems to have such different experiences with the same fish.

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