Matthew D. Laudato writes about software and technology


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With all of my tech blogging, I sometimes forget that I have other interests and hobbies. One of those that has developed is keeping an aquarium, spurred in equal parts by my son’s love of living things and my father’s many impressive tanks that he has kept over the years.

In that spirit, this page is dedicated to fish tank technology, and more specifically, notes and tips on keeping a goldfish tank. The information here is mostly empirical – I’m basing it on my experience over the past 2 years plus on general knowledge of biology. Keep a look out on this page for information dedicated to our scaly friends!

Chick, Goldie and Flip

These three have been with me since the beginning. Chick is the Ryukin on the left, Goldie and Flip are comets. They are about 2 years old.

No fishbowls!
The first rule of keeping goldfish is no fishbowls. Fishbowls do not provide enough room or air for goldfish, plus since there is no filtration, you’ll have to change the dirty water frequently. And all those water changes will result in little or no permanent bacteria colony – a very important part of your tank.

Tank basics
Choose a good size tank for goldfish. My 29 gallon ‘euro’ style (tall with a curved front) is almost too small for the 3 fish I keep. Goldfish get large and are dirty, so 3 is the maximum for a tank this size – around 10 gallons of water per fish. I bought a very nice looking stand that is made for this style tank, that has 3 open shelves and a glass door compartment (where the air pump resides, see below). Total for the tank and stand was around $300 at PetSmart.

Fish need oxygen to survive, which they get through their gills from the dissolved oxygen in the water. Generally, the normal action of filtration (specifically the splashing of water from the filter back into the tank at its surface) provides plenty of aeration. I opted to also install two 3″ air stones, buried under the rocks. I power them with a single ’40 gallon’ pump. My pump has a single outlet, so I also bought a metal T-valve to split the air into two flows, one for each of the air stones. The pump, stones, tubing, tubing clamps (to secure the tubing to the inside of the tank) and valve should cost you around $40 or so.

For goldfish, the substrate needs to be either very fine or very coarse. Goldfish have big mouths, and twice earlier in my tank’s history I had to pull Goldie out and remove a medium sized rock that had gotten stuck in his mouth. He would not be here today had I not acted. Currently I use large aquarium stones, too big for even a big Goldfish to put into its mouth. The smallest stones are at least 1 inch in diameter. I like them better than sand for aesthetic reasons, plus they provide good surfaces for algae to grow (yes, some algae is a good thing. More on that later). The lesson is: don’t use that pea-sized gravel that you see in the pet shop. Sand or rocks, and nothing in between. Two 5 pound bags of ‘River rock’ will set you back around $10 at most suppliers, and should be more than enough. Just make sure to pick out any smaller rocks that could get caught in your fish’s mouth.

Keep it simple. Resist the temptation to over-decorate. I have one underwater ‘bridge’ in my tank, that has 3 ‘tunnels’ – ideal for giving the fish a place to hide, rest and stay out of the light during daytime. Remember, goldfish need a lot of room, so give them a hiding place or two, but don’t overdo it.

Goldfish as I have mentioned before, are dirty fish. That means that they are not efficient at processing food into nutrients. Put another way, they poop a lot compared to other fish. When I first set up the tank I had a single Top Fin Power Filter 40 from PetSmart. This proved to be too little filtration – the filter bags were clogged every week or so, and the tank never really looked clean. After a while, and after doing some reading, I went out and bought a second Power Filter 40, and the tank has been perfect ever since. I can go for a 3-4 weeks without cleaning the filter bags, and the water is clean and clear. The lesson is: if you’re keeping goldfish, more is better when it comes to filter power. Keep the filters running 24 hours a day, no exceptions.

One note about changing the filter bags.  On the Top Fin models, it is easy to tell when its time to change bags. Water normally exits the filter back into the tank from the large wide trough. When you start to see water exiting from the smaller trough where the suction pipe is, it’s time to change the filter bag. Just follow the instructions and you’ll be fine.

Setting up the tank
Once you have your tank on its stand, take a moment to look at the tank and its placement in the room. Once you fill the tank with water, it is immovable, so now is the time to change your mind about where you want the tank. Then set up the tank as follows:

  • Install the air stones, tubing and place the air pump on a shelf below the tank (hidden if you have a compartment with a door).
  • Add the rocks. Just enough to cover the air stones is fine.
  • Add any decorations.
  • Fill the tank with water tap water.
  • Install the filters.
  • Install the hood and lighting.
  • Plug in the filters, air pump and hood light, and make sure that everything is operational. Consult the manuals for your equipment, or leave a comment on this page – I promise to get back to you.

    Congratulations! Your tank is on its way to being fish-ready. Notice that I do not include a heater. Goldfish are cold water fish, so you don’t need a heater – another benefit for the novice aquarist.

    Choosing fish
    It is a good idea to leave the tank empty for a few days, even a week, with the filters running. At this point, go to your local aquarist and buy 2 comets. These are feeder fish that people who keep carnivores such as Oscars will buy to feed their meat-eaters. They are cheap (usually no more than 35 cents each), hardy, and in their fish way will certainly appreciate being used as pets rather than as pet food. When you get home place the bag containing the fish in the tank, open it up, and let the bag float for 20 minutes to let the temperature equalize with the tank. Then gently open it into the water and let your fish free.

    Feed your goldfish lightly. I feed mine once a day in the morning, typically no more than 1/4 teaspoon of food. Since Goldie is over 6″ long and well, fat, I suspect that this is even too much. Overfeeding is bad for several reasons, but the biggest one is cleanliness of the tank – more food means more goldfish bowel movements. I have a feeding ring, which the fish will crowd around once they see me in the morning. I give them a variety of food day-to-day: goldfish flakes, small goldfish pellets, and frozen brine shrimp (once a week for the shrimp). Any flies, mosquitos, spiders or other creepy-crawlies that you would rather not have in your house will also be a treat for the goldfish. If you catch them, your goldfish will certainly eat them with no ill effect.

    All heathy fish tanks have algae. How much algae you should allow to grow is mostly a matter of personal preference. I let algae grow freely on the substrate and on the rear wall of the tank, but I keep the front and sides clean using a magnetic cleaner. Usually about once every ten days is sufficient for clearing the algae. Algae is good for your tank on several levels. First, it’s green and thus photosynthetic – it uses light and goldfish waste (really, the nitrates that the waste breaks down into) to produce its food, and releases oxygen like any other plant. Second, it is edible, so the fish can graze on it. Finally, it is natural and thus all good – so don’t clean algae obsessively. Let some of it grow and come into balance with your fish and the bacteria that live in the tank.

    The next time I update this page, I will add a maintenance section.

    Updated 11/14/2009.


    Written by Matthew D. Laudato

    November 14, 2009 at 2:18 pm

    One Response

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    1. Thank you for a wonderful post. I enjoyed it.

      Mariela Trogdon

      July 25, 2011 at 3:26 pm

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