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Overfeeding Your Aquarium – A Common Mistake and Its Consequences

fish foodsOverfeeding your aquarium is one of the most common mistakes made by aquarium hobbyists, and it isn’t one only made by beginners. It’s easy to go overboard when our fish “always seem hungry” and even appearing excited when they see you coming towards the tank with food in hand.  Healthy fish pretty much always look hungry. It also doesn’t help that we’re directed by packaging instructions to feed amounts that may be inappropriate for the type and number of fish we are keeping. We want the best for our fish and we want to be successful in keeping them, but it’s easy to cross the line from feeding enough to feeding way too much.

Problems Caused by Overfeeding

Leaving uneaten food in the aquarium is never a good idea. Watching food fall to the bottom of the tank, with the thought that your fish to eat later, can lead to big problems. Many fish are kind of programmed to eat food at certain places in the tank. Surface feeders, column feeders and bottom feeders tend to feed within their comfort zones, so you won’t typically see surface feeders travelling to the gravel for a snack, and fish that feed in the water column usually ignore food bits after they settle. No matter what kind of fish food you distribute, pellets, flakes, frozen foods or even live feeders, anything not eaten is left to decay. This unprocessed food, in addition to the waste produced by the food that is actually digested, can quickly create issues with your tank’s water chemistry and/or cause a bloom in the population of naturally occuring scavengers.

Uneaten foods quickly start to decay, adding to ammonia and nitrate levels of the aquarium, and it can very easily result in more bacteria than the nitrogen cycle can handle causing cloudy water. Overfeeding is not only dangerous to the health of your fish, but it causes unnecessary demands on your filtration, often resulting in poor water quality. Fortunately, the problems that arise from overfeeding are quickly and easily reversed or eliminated once you get your feeding habits under control.

Aquarists are also often shocked or full of disbelief when we tell them that the hordes of unsightly little “bugs” or worms creeping up the glass and through the rock and substrate are a probably a result of over-feeding their aquarium. What you see are probably either scavenger nematodes or planaria. Chances are there were a few of these critters in your tank from the start. They can be introduced via fish, plants, wood or other things you add to the aquarium as their microscopic eggs can travel on any of these things. They are generally harmess, but when you overfeed the opportunity arises for their populations to boom with the abundance of decaying matter in the substrate. Reducing the frequency and amount of food will help to bring the population back down to size, but you may also choose to treat the tank with anti-parasitic medications to speed the process along.

Tips for Proper Feeding

When it comes to feeding your aquarium fish, your main goal (besides providing them with good variety and nutrition) should be to make sure they eat everything you feed them. Package directions usually recommend that you feed as much food as they can eat in however many minutes that manufacturer deems correct.  Generally, the recommendation is far more than necessary for the average aquarium, stating that you should feed as much as your stock can eat in 2 to 5 minutes. Chances are your fish will eat all they need in a fraction of that recommended time. With close observation you can tell when they have had just enough, and you have to get a feel for the difference between the fish being hungry and ready/able to eat, as opposed to eack fish swmming instinctually after something dropped into the aquarium.  Many foods also recommend multiple feedings in a day, but feeding your aquarium fish once a day or even once every other day may also be fine, depending on type of fish you keep. Some fish may need to be fed multiple times each day, too!  The idea is to get to know the fish in your tank and their needs and habits, as opposed to feeding blindly as per packaging instructions.  The frequency and amounts you feed are largely dependent on the types of fish you keep and the types of food you’re feeding.  Don’t worry too much about underfeeding when you cut back. Fish in aquariums get more food, with less work, than would ever be the case in the wild. The risks to your fish from overfeeding are greater.

pleco eatingInappropriate feeding can be as detrimental as overfeeding, and inappropriate can mean a couple of different things. While providing a varied diet is important for vibrant and healthy fish, it is also important to become familiar with appropriate food offerings for the species you’re keeping in regards to type and size. Commercial diets like community flakes, granules and pellets provide balanced nutrition for a variety of fish, but there are also freeze-dried, frozen and live food options to supplement any size and species that aid in mimicking a more natural diet for the animals that are in your aquarium.

Try to have an idea what your fish would eat in their wild habitat to guide you in foods to offer them. Some fish are predators (meat eaters), some are herbivores (plant eaters), most are omnivores that will eat both plant and animal matter.  Some fish have specialized mouth parts for feeding a certain way; surface feeders have upturned mouths and prefer floating foods, bottom feeders have downward turned mouths and prefer foods that sink to the floor of the tank, ect. The majority of aquarium fish are column feeders, and they feed on bites that stay suspended longer in the water column.

Food size is also important. Offering foods that are too small for your fish will require larger and more frequent feedings, and much of the food will be missed, ending up in the gravel. Foods that are too large for your fish will also go to waste. Large, hard foods may be too difficult to break or swallow, and can even injure delicate mouth parts or internal anatomy. Offering delicate foods like flakes or granules to small fish is generally safe, and larger pellets and whole foods whether frozen, freeze-dried or live, can work out well for larger predatory species. Commercial fish foods available in your local fish store provide high-quality nutrition for your aquarium fish. Dry foods can be supplemented with with some frozen or freeze-dried variety three or four times a week to add interest.

Once you’ve gotten a handle on the types, frequency and amounts of food you offer, you’ll be ahead of the game. Follow a regular maintenance and water change regime, as well. Siphoning your substrate to remove any leftovers and fish waste is a vital part of keeping your habitat clean and healthy.


  1. avatar

    Hello Mr. Indiviglio

    I’m concerned my red claw crayfish isn’t getting enough to eat and is chewing on the plastic plants as a result. My tetras are eating all the food when the lights are on and the catfish is mopping up the pellets before he can when they are off. How can I ensure he is getting enough to eat?

    Cheers, Alex

  2. avatar

    Alex, you could try some target feeding techniques if you feel that your crayfish is not getting enough food. There are several types of products for target feeding, you can use aquarium tongs, or a feeding prong, to hand food directly to the crayfish, or you can use a tube to drop sinking pellets down to the bottom of the aquarium so that the fish can not eat the food on the way down. Undergravel filter replacement lift tubes work well for this, and are clear so you can see the food, or you can simply use a section of PVC pipe. Hope that helps.

  3. avatar
    Erin Stepenoff

    We just got a 5 gallon tank for our betta. Fluval 5 gallon tank. Got it set up with substrate and a few live plants and it looked great.
    Then we went on vacation for 5 days and unfortunately left a feeding block in and my daughter left the attached LED light on the whole 5 days. When we hit he the tank was growing white cloudy/slimy grassy like stuff on the substrate and tank smells bad.
    What now?
    The smell is very bad. Is it dangerous for us or the fish?
    How can we fix it?
    We know now to separate servings of food and get a friend in to feed every few days next time and to keep the light off.
    We are so sad. We are new to keeping an aquarium.
    Thank you for your time

  4. avatar

    Hi Erin, It sounds like the food or other material in the tank is decomposing and may be causing some fungus to grow in the tank. Anything decomposing in the tank cane certainly effect the water quality and make it unhealthy for the fish. Have you tested the water quality – Ammonia, Nitrite, Nitrate, pH to start with? I would certainly recommend doing a water change and using a gravel vacuum to clean any debris out of the substrate. What type of filtration do you have on the tank? If you have any carbon in the filter, I would change that to help get rid of the smell and any waste in the water.

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