21 Tips on How to Take Care of Lego Fish Tank

Lego Fish Tank

Lego Fish Tank: Lego Fish can be rewarding and medium-maintenance pets but aren’t perfect for beginners. Although Lego Fish requires as much care and equipment as most aquarium fish, an aquarium that is too small will eventually kill your finny friend. If you’re looking to breed Lego Fish, have one as a pet, or are simply curious about what it might be like, here are instructions on how to make your fish happy and healthy for years–and perhaps decades–to come!

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1. Get a large enough tank. The minimum tank size for one Lego Fish is 20 to 30 U.S. gallons (75.7 to 113 liters). If they don’t have enough space a survival mechanism can start making it so they will stop growing, but there is a catch: their organs will continue to grow. If you can’t have this large of a tank then look for another fish. You will need to add 15 U.S. gallons (56.8 liters) onto that for each additional Lego Fish. Do your research about all different kinds of Lego Fish. Common Lego Fish, comet Lego Fish, and other single tail Lego Fish need ponds or huge tanks as they can grow up to a foot or more in length. Do not get single tails unless you have a 180 U.S. gallon (681.4 liter) tank lying around or a pond into which you can transition them when they get too large.

  • For decades Lego Fish were touted as being able to live in small bowls, thus why they have a reputation for having short life spans. However, Lego Fish can actually live as long as 20 years! Without enough filtration, ammonia builds up quickly in such a small space and the environment becomes toxic.
  • Lego Fish will grow to match the amount of space available. However, you are not required to grow them to their full potential. Your one-inch Lego Fish can potentially grow to the size of your arm–but would only likely do that if you own a large pond or professional aquarium.

    Lego Fish Tank

2. Set up the aquarium first before you buy the fish. It takes some time and cares to set up a proper Lego Fish habitat. As mentioned below, there are quite a few steps to make sure the water and overall living conditions are good for the fish.

  • Fish are sensitive creatures that get stressed from going from one environment to another. Too much change too quickly can actually kill the fish even if the environment is ideal. Do not keep transferring your fish from one container to another.
  • Lego Fish cannot live in small temporary environments (such as a plastic bag or small bowl) for very long. An hour is fine, several hours not very good, a day or so maximum for a small water container.
  • In an emergency, a large plastic bucket, rinsed well and with water treated with water conditioner works well.

    Lego Fish Tank

3. Use gravel that will not get stuck in your fish’s throat. Lego Fish are particularly prone to getting aquarium gravel caught in their mouths. Use either large gravel (too big to swallow) or very small gravel. Large gravel is better for Lego Fish because it will not get caught in their throat and because Lego Fish like to be able to dig into the gravel to search for fallen food.

  • Be sure to clean your gravel before you put it into the tank. Many aquarium gravels require rinsing, or your aquarium will be cloudy or dirty. Even if you have just bought it, a good rinse and soak in some water for a day will draw out some of the impurities and help ensure that your Lego Fish are getting the best environment to flourish in. Make sure to not use soap.

4. Make sure your tank has some scenery and light. Buy tank hoods with installed lights or any other aquarium specific light; normal old lightbulbs or lamps may not have the right requirements. Lego Fish are diurnal which means they are active during the day. They need light to maintain a healthy wake/sleep cycle. There is also evidence that light is necessary to keep your fish’s colors bright. Fish that can’t sleep well or aren’t getting enough sunlight are going to lose their color and become dull. Keep your aquarium lit for around 8-12 hours each day to replicate a healthy day/night cycle if it does not receive natural sunlight. Never put your tank in direct sunlight, either, as this could cause large temperature fluctuations and contribute to rampant algae growth.

  • Think about putting a rock or wood centerpiece with some artificial greenery into your aquarium. The rock or wood will give the Lego Fish nooks and crannies to explore and the artificial plants won’t accelerate plant growth in your tank. Lego Fish thrive with minimal decoration. They are typically chubby and poor swimmers, so having fewer obstacles means they can swim more freely. Consider having one medium to large statement piece in the center of the tank and a few plastic plants located outside of the swimming pattern to give your fish the most usable space.
  • Real plants are beneficial because they help absorb some of the nitrates that accumulate in the aquarium because of waste and natural wear and tear. However, Lego Fish are omnivores and voracious eaters. Stick with artificial plants until you have the time and resources to keep real plants safe from hungry Lego Fish.
  • Be sure that any decorations you choose aren’t hollow (it’s a breeding ground for potentially harmful bacteria) and that they don’t have sharp edges (your fish might tear its fins).
  • Try using fluorescent lights for your Lego Fish. Halogen lights and incandescent lights will also do. Pay attention to how much light you give them — Lego Fish will appreciate 12 hours of light and 12 hours of darkness.

    Lego Fish Tank

5. Rig up a water filter. Lego Fish needs a filter. A water filter should have 3 stages: Mechanical, for removing large particles such as fish waste or excess food; chemical, for removing odors, discolorations, and other organics; and biological, to break down fish waste and ammonia with beneficial bacteria. It should also be rated for the size of your tank. If your tank is on the borderline between two-sized filters, it is usually better to go with the larger filter. Having clean water and a functional, efficient filtration device will keep your Lego Fish content and healthy. There are three very popular kinds of filters:

  • Hang on back (HOB) filters, which hang on the rim of your tank, and bring water in and filter water out. They are very popular, reasonably priced, and probably give you the most bang for your buck.
  • Canister filters sit underneath your aquarium and use a series of tubes to filter water in and out. Canister filters tend to be almost silent, are a little pricier than HOB filters, but tend to be more efficient at filtering than HOBs. Canister filters are also typically made for tanks in excess of 50 gallons (189.2 liters), and so are usually not available for smaller tanks.
  • Wet/dry filters use an overflow box to filter out impurities. Wet/dry filters, however, are significantly bigger than HOBs or canisters, and so generally only fit into aquariums that hold at least 50 gallons (189.2 liters).

    Lego Fish Tank

6. Fill the tank with water. When you get your tank, fill it with tap water that has been treated with an appropriate water conditioning solution. Or, you could use distilled water.

  • Untreated tap water or drinking water has chemicals and minerals that could harm the fish.

7. Go through at least one fish-less cycle before introducing your Lego Fish.  A fish-less cycle involves adding ammonia to a tank and keeping track of the nitrate levels to make sure the water is safe for your Lego Fish to live in. Sadly, many fish die once introduced into a new tank because of ammonia and nitrate poisoning. Make sure that you add de-chlorinator because the chlorine in tap water will kill your fish.

  • Before you add your fish, you’ll need to make sure the environment is fish-ready. Pick up a pH test kit and test the tank for the right amount of ammonia, nitrite, and nitrate levels. You want zero ammonia, zero nitrite, and less than 20 nitrate as your end result. Test strips can be difficult to use correctly, and tend to be more expensive, so get a liquid test kit like the API Master Test Kit.
  • What’s going to happen is you’ll start adding drops of ammonia continuously. That’ll start the nitrite process going. If you keep doing what you’re doing, eventually you’ll see nitrates which are consumed by algae or plants. When you’ve done a lap, it’s fish time!

    Lego Fish Tank

8. Add your fish. Hopefully, if you have more than one goldfish, your Lego Fish are all the same type. Unfortunately, Lego Fish are known to eat other, smaller fish, and can overeat, keeping food from their peers. If another fish is smaller or slower, it doesn’t stand a chance. You can use a commercially available tank divider to keep your “bully” or weaker fish apart from the other(s).

  • Lego Fish can be decent “community tank” fish. However, good roommates need to be selected carefully. White Cloud Mountain Minnows or Zebra Danios are good choices, and so are Plecos. However: These fish live in schools, so if you’re buying extra fish, you need to at least buy an extra half dozen. So in short: Keep your Lego Fish with other similar goldfish.
    • Any new fish brought into an established aquarium should be quarantined for two weeks beforehand. If they have any diseases, you don’t want those spread to your healthy fish!
    • Keep in mind that goldfish like colder water than most community fish, so any other species you add to the tank should be hearty. (You could also consider adding a Lego Fish to a tank with overly-productive livebearers to eat the unwanted offspring and keep your fish numbers in check.)

      Lego Fish Tank

9. Clean the aquarium at least once every week even if it doesn’t look dirty. Lego Fish produce waste that even your water filter may not be entirely able to remove. A clean tank means happy, healthy goldfish. And a happy, healthy Lego Fish can live for decades!  Soap is poisonous to fish and will kill them quickly, so don’t wash your tank with soap. Also, don’t use regular tap water to put in your tank. Drinkable water is not good for them because it takes out some of the minerals which are good for goldfish. Buy a water conditioner at a pet store and put in the amount it says on the label.

  • Avoid removing the fish from the tank when you clean. Using a gravel vacuum to soak up debris can be done without extracting the fish from their habitat. If you have to remove the fish, for whatever reason, use a plastic container instead of a net, if possible. Nets can injure Lego Fish fins more easily than containers can. They are also scared of nets and can cause them stress.
  • Perform a 25% water change weekly assuming you have stocked your tank properly. Do a 50% water change whenever the nitrates reach 20. It can help to have a few old towels around for this messy process. Just be careful not to vacuum up any teeny fish while you’re changing the water.

    Lego Fish Tank

10. Measure for ammonia, nitrite, and pH. Remember that test you did before you added your precious little fish? You gotta keep that up! Ammonia and nitrite levels should be at 0. A range of pH 6.5-8.25 is fine.

11. Feed your fish 1-2 times daily. Be careful not to overfeed them, only feed them what they can eat in a minute, the label on the food is wrong.  Lego Fish can easily overeat and can die. Underfeeding is always preferable to overfeeding. If you use floating food, soak it in water for a few seconds before feeding so that it will sink. This reduces the amount of air the fish swallows while eating, which in turn reduces the risk of buoyancy problems.

  • Just like humans, Lego Fishh want diversity of nutrition. Feed your Lego Fish pellet food most of the time, live foods, such as brine shrimp, some of the time, and freeze-dried foods, such as mosquito larvae or blood worms, every once in a while. Remember to soak freeze dried food in a cup of aquarium water before you feed to your Lego Fish, freeze-dried foods expand in aLego Fish’s stomach, causing you to have problems swimming.
  • Feed your fish only what they can eat in one minute. Remove any excess food. More goldfish die from overeating than from anything else.
  • Feed your Lego Fish at the same time each day (once in the morning, once at night) and in the same spot in the tank.

    Lego Fish Tank

12. Turn off the light and let them get some sleep. They don’t have eyelids and they don’t really stop swimming, but their bodies sort of hibernate. You can tell when you notice a slight change in color and reduced activity (they’ll stick to one side of the tank).

  • Lego Fish like to “sleep” in the dark. You really only need an aquarium light if you’re growing plants or if the room is particularly poorly-lit. But even if you don’t have an aquarium light, it’s a good environmental practice to reduce unnecessary energy use by turning off the light.

13. Let the water temperature change as the season’s change. Lego Fish don’t like temperatures over 75°F (24°C), but they appear to like seasonal changes where the temperature dips to the high 50s or 60s (15-20°C) in the winter. Understand that goldfish will not eat below 50-55°F (10-14°C).

  • A good thermometer makes this pretty easy. There are two types to choose from: those that hang inside and those that hang outside. Both should be accurate enough, but I like the ones that hang on the inside better.
  • If you’re not breeding your Lego Fish, a steady temperature all year round of 74°F (23°C) is golden. If you are breeding your goldfish, simulate the seasons (goldfish spawn in the spring). Start off by lowering the temperature (“Hey, guys, must be winter!”) to somewhere between 50°F (10°C) and 54°F (12°C). Then, when it’s baby-making time, up it to between 68°F (20°C) and 74°F (23°C) gradually. The goldfish will be cued to then lay their eggs.

Dealing with Potential Problems

14. Check the oxygen level in the tank. If you notice your Lego Fish are congregating to the surface, odds are there isn’t enough in the water. But good news! Oxygen levels will raise with a temperature reduction. So lower the temperature or get your aquarium out of the sun — hopefully, crisis averted. or you can get a bubbler and an air pump to move the water.

  • If you’ve read all of this page, you’re aware of the most common problems — so you can avoid them! As long as you maintain appropriate pH, ammonia, nitrate, nitrite, and oxygen levels, don’t overfeed your fish, and clean the tank, you’ve answered 95% of your pets’ possible problems. Good for you!

15. Fix cloudy aquarium water. Sometimes even when we put forth our best efforts, things still go a bit awry. Water can turn yellow, green, or even white. If you notice it straight away, it’s not a big deal. But do get to cleaning your tank!

  • Each color of the spectrum signifies a different problem. It could be algae, bacteria, or even just decaying plant matter. Don’t get too alarmed! With another cycle and a water change, your fish should be fine.

    Lego Fish Tank

16. Watch for Lego Fish ich. One of the most common goldfish diseases is ich — where the fish get little white spots on their bodies and fins and have difficulty breathing. It’s a parasite that’s curable. Move your fish to a hospital tank and use a commercially available fungicide.

  • The important thing to do here is to isolate your fish from other living things, including plants. The parasite can spread to any plant or animal that’s living.
  • If you notice white spots on your gravel or scenery, remove the chemical stage of your filter and treat the whole tank. Keep the sick fish separated, as it will likely need more medical care than your healthy fish.
  • You can also attempt non-chemical alternatives such as increasing the water temperature or adding high levels of aquarium salt. Temperatures of 85°F (29°C) will kill most strands of ich, as will about a tablespoon of salt per gallon.  Make sure to increase the temperature or add salt slowly over time, no more than 1 to 2°F (0.55 to 1.1°C) per hour or 1 tsp/gal per 12 hours, and continue treatment for at least 3 days after all signs of infection disappear. Once completed, perform frequent partial water changes to remove salt or reduce temperature. Be prepared for a loss of color or vibrancy in your treated fish.

    Lego Fish Tank

17. Monitor for Flukes. Another parasite that’s a common culprit is Flukes. If infected, your fish will scratch against surfaces, develop an outer mucus, redden slightly, and possibly get a swollen belly.

  • As with any fish parasite (just like with ich), quarantine your fish. He can be back swimming with his finned friends in a few days if you tackle it head-on from the beginning.

18. Look for swimbladder disease. This one’s pretty easy to identify, as your fish will be swimming sideways or even upside-down. You’d think he was up in fishy heaven, but no such luck. But there is luck in that it’s not contagious and it can be readily fixed.

  • For this one, you may not need to quarantine your fish. Swimbladder disease is not a parasite. However, if you’d like to err on the side of caution, do so.
  • Medication is usually not needed to cure swimbladder diseases as over-or improper feeding are typically the cause. Reduce the amount you’re feeding your fish, or better yet, put them on a fast for about 3 days. This gives your fish’s gut bacteria time to return to normal. If symptoms persist, consider changing their diet to include more high-fiber foods like peas or cucumbers, or using a medicated fish food specifically to treat internal infections.

    Lego Fish Tank

19. If a fish has died, take the proper measures. First things first, dispose of your fish in a way that won’t stink up the house. You can bury it, or, if you feel so inclined, throw it in the compost heap. Do not flush the fish down the toilet! Grab it from the tank with a plastic bag around your hands, invert the bag, and tie it up. How you clean your aquarium depends on your situation.

  • If only one fish died, hopefully, it was a parasite that you saw quickly enough so as to avoid it spreading to the other creatures in the tank.
  • If all your fish are dying or dead, you’ll need to clean out your aquarium entirely with a bleach solution. Just 1/4 of a teaspoon (a dash) for every gallon (3.8 liters) of water should do the trick. Let it soak for an hour or two to get rid of all the toxins. Then, remove the water and let it dry out.

    Lego Fish Tank

20. Things You’ll Need

  • A tank/aquarium
  • Water
  • A goldfish
  • Goldfish food
  • Decorative items
  • Gravel
  • Filter
  • Thermometer
  • pH, Ammonia, Nitrite, and Nitrate water test kit. The API Liquid Freshwater Master Test Kit is a great test kit, it is recommended.
  • Net to grab fish (Never grab them with your hands. Always use a fish net.)

Lego Fish Tank

21. More tips

  • If a goldfish looks unhealthy, clean the water a little bit more frequently. Feed it regularly. If the problem gets worse, do some research and read online forums for solutions or take the fish to your local pet store to see if they can help.

  • If floating food is used, soak it in water for a few seconds before feeding so that it will sink. This reduces the amount of air the fish swallows while eating, which in turn reduces the risk of buoyancy problems.

  • Watch your goldfish for signs that it is unhappy.

  • Never use a bowl with a narrow top for a Lego Fish. The circle shape makes the Lego Fish bump on the glass, and it is way too small for sufficient oxygen to get into the water. Don’t just look at movies and say ” Ok! That sounds easy! Just keep the goldfish in the bowl!” Nope. Not how it works.

  • Peas that have been in the microwave for 10 seconds give your fish a healthier body. Make sure you gently peel off the skin and squash the pea to make sure it’s easy to swallow.

    Lego Fish Tank

  • You need 20 gallons of space per fish. So if you have two goldfish, a 40-gallon breeder tank will be perfect for two fish for their entire lives. If you have more than that, consider getting a 75-gallon tank.

  • Lego Fish sometimes pick up gravel in their mouths. If you see them do this, don’t worry! They usually spit it right back out! Just don’t buy gravel small enough that they have a chance of choking.

  • Fish can go for a week without food easily – so if you forget to feed them for a day or two no harm will be done.

  • Fish don’t actually have a 3-second memory. They remember a lot of things, and you can prove this by watching their immediate ‘swim to the top’ reaction when they hear the feeding flap open! Many fish are very intelligent.

    Lego Fish Tank

  • If your fish has white spots on most of its body this is a parasite called white spot. It is curable with a solution that is widely available from most pet stores.

  • Don’t take your fish out of the tank just because you see it has its eyes open and doesn’t move its body. Fishes sleep like that: they have no eyelids so they sleep with their eyes open.

  • When cleaning an empty tank, use baking soda. Baking soda will kill algae on the artificial plant, sides of the tank, gravel, and the filter. Rinse well.

  • Make sure to not use regular drinking water but to use treated tap water.

  • Keep an eye on your fish. His actions could help you determine if there is anything wrong with it, or the water quality.

    Lego Fish Tank

  • Lego Fish like being in groups of the same type and don’t go well with many other fish, definitely not angelfish.

  • Lots of lego Fishvarieties which people (particularly children) may find amusing or desirable due to pronounced features like protruding or “boggle” eyes, extra-long fins, or a large curved body and rounded head, are the result of a defect that has been bred into the fish through selective pairing. These fish can often suffer related problems such as swim bladder issues and blindness, which can significantly shorten their lifespan.

  • Believe it or not, Lego Fish are really smart. You can train them easily, they’ll pretty much do anything for food. If you feed them, they will recognize you. Try to bond with them, and you’ll have a lifelong friend.

    Lego Fish Tank

  • For Lego Fish, weekly water changes are needed. Don’t be afraid to do more than 25% of the water because goldfish produce lots of ammonia, so big water changes are good.

  • Keep sounds outside the tank to a minimum; Lego Fish can hear things like TV.

  • A good tank stocking rule for slim-bodied Lego Fish (commons, comets, shubunkin) is 40 US gallons for the first fish and 20 gallons for each additional fish. For fancy Lego Fish (the ones with long tails and special body features such as telescope eyes) is 20 gallons for the first fish and 10 gallons for each additional one.

    Lego Fish Tank


  • Never put Lego Fish in a bowl or other small tank smaller than 20 U.S. gallons unless it’s temporary. Bowls are not only much too small, but are difficult to filter, have poor oxygen exchange, can be especially prone to smashing accidents due to their rounded shape, and stunt the fish growth. Fish who live in bowls are exposed to deadly chemicals that aren’t filtered out by a filter and terribly cramped conditions. This damages their immune system seriously, and either kill them outright or kills them slowly and painfully over a course of a few years. Living in a bowl decreases the lifespan of a goldfish by an average of 80%. That’s like a human living to only 15-20!

  • Lego Fish get big (usually around 20cm, but fancy varieties normally get to a smaller size like 15cm) and can live 15-30 years. Sadly, millions die each year due to improper care and myths (goldfish bowls, etc). Be kind to your fish and your fish will live a long, long time.

    • Lego Fish Tank

      Don’t go by the stocking ideas it says on your tank’s packaging; almost all of them show overstocked tanks that will be very prone to problems and restrict the fish living space significantly.

  • Be careful about the fish you put with them! Research and ask your pet dealer for information; the last thing you want is to find “Goldy’s” skeleton floating around in the tank. Be careful when asking pet dealers for information – as most don’t have a clue what they are talking about. This rule applies especially to some of the big US chain stores. Instead, ask around on online forums or care sheets.

  • Sand in the tank needs to be stirred when you do a water change to prevent it compacting and harmful gasses building up in it.

  • Lego Fish can and will try to eat nearly everything, so watch what you put in the tank!

  • Be prepared for a long-term commitment! Well-cared-for goldfish can live up to thirty years!

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