Starting a New Aquarium (or restarting an old one)

You’ve got a brand-new aquarium kit with the whole works – filter, heater, canopy, lights, tank (of course!) and maybe even a fish net, some flake food, water conditioner and a little booklet to tell you Everything You Need to Know to Keep Fish.

Or maybe your friend or your sister gave you an aquarium with a bunch of stuff in it and said, “Here, I have no room for this.” and you thought, “Cool! I’ve always wanted piranhas!”

Now what?

Here are the basic steps to setting up a new aquarium. By “new aquarium” I mean any aquarium, new or used, which has been without fish for more than six weeks. It doesn’t matter if the tank is new or used, or if there were fish in it before.

1 – Water

Set your tank up where you want it. Once you’ve filled it, it’s going to be hard to move. Water weighs eight pounds per gallon, so a twenty-gallon tank will be about 160 pounds once it’s filled. Even if you could pick it up, it’s a glass box, and the  bottom will probably crack.

If you’re using city water, you’ll need a dechlorinator. This is a chemical that takes the chloramines out of the water. Chloramine is a combination of chlorine and ammonia, which cities use because it persists, keeping the water chlorinated right out to the outskirts of a large city. Chlorine will dissolve out on its own, but chloramine will not.  Dechlorinators are also called “water conditioners”. Prime can be used at a rate of two drops per gallon.

If you are on well water, you may need to remove iron from the water. If you suspect your water is particularly high in iron, get it tested. Compounds to remove iron are available at pet stores.

2 – Light, heat, filtration

Now that your tank is filled, put in the filter and heater.

The filter will either be a submersible one, or, more likely, a hang-on-tank (H.O.T.), which hangs on the back of the tank (surprise!) It will have an intake tube extended into the aquarium, and a reservoir with an overflow. Follow the directions on the kit and install the filter, then plug it in.

The heater will almost certainly be submersible. Check the directions on the box. Always have the heater in the water before you plug it in, and never take it out before unplugging it and letting it cool down.  For a tropical tank, set the temperature between 74 and 78 degrees Fahrenheit.

Don’t use a heater for goldfish. Almost everything else requires one.

The canopy goes onto the tank. Unless you have live plants in your aquarium, the only time you really need your tank lights on is when you want to watch the fish. You can turn the lights on in the morning, or even when you get home from work. Turn them off at night. Everything in nature gets a day and a night, and it’s not good for your fish to be lit up all the time.

3 – Furniture

Substrate (gravel, rocks, sand, whatever you choose to put on the bottom) doesn’t need to be really deep as a rule. Depending on what kind of fish you plan to keep, you can often manage with a very thin layer for colour.

Most fish feel more secure if they have hiding places, so plants, caves and pieces of wood are a good idea. If your fish feel secure, they’ll be out more often. They’ll also be more relaxed, so they’ll be brighter and more active.

Remember that the fish you buy in a pet store are almost always juveniles. Fish grow, and that cute little castle may be too small in a year, and allow your fish to get stuck and injured.

4 – Fish

Here’s the fun part – stocking your aquarium.

First, I want you to take a good look at the box. See how many fish are in the aquarium on the box? Chances are you can’t keep that many fish in yours, especially if it’s a one-gallon or two-gallon tank. The box is not a reliable guide to how many fish you can keep.

Here’s how many fish you can keep in an aquarium:

For every gallon of water, one inch of slim-bodied fish (like neons, comets, zebra danios)

For every gallon of water, one-half inch of fat-bodied fish (fantail goldfish) or deep-bodied fish (silver dollars, angelfish, discus).

This means that if you have a 20-gallon tank you’re allowed 20″ of slim-bodied fish or 10″ of fat- or deep-bodied fish, maximum.

You can’t get them all at once.  There are bacteria that digest fish waste, but they only reproduce when there’s fish waste for them to eat. This means that a new aquarium has hardly any. (For more on this, see the Aquarium Maintenance page.) You have to start small, with no more than 20% of the maximum capacity of your tank.

So for the 20-gallon tank, you can have four inches of slim fish, or two inches of something like angelfish, to start.

If the fish are alive at the end of two weeks, you can add that much again. Continue until you have 80% of your tank’s capacity, because you need to leave some room for the fish to grow.

Basic Maintenance

Do a 10% water change every week. Take out 10% of the water and replace it with new water.

Topping up from evaporation is not a water change.

Feed your fish only as much as they will eat in one or two minutes, and only once or twice a day. It won’t hurt them to miss a day. Rotting food also releases ammonia into the water.

If you rinse your filter sponge, do it in tank water, not in chlorinated water. Chlorinated water kills bacteria and sets you back to square one.

Troubleshooting while setting up

The water may get cloudy. This is because the bacteria are not yet up to a high enough population to handle the fish waste. Do not clean out your tank and change all the water! If you do this, you’re starting again at square one.

Instead, do a 10% water change a couple of times a week and don’t add any more fish.

If your fish come to the surface and gulp air, the water is low on oxygen. Do a 25% water change. Don’t add any more fish. Check that your filter is working and is large enough for the tank – if it isn’t, get one that is.

You can add an airstone and air pump if you like, but the filtration should be enough to oxygen ate the water in most aquariums.

You can add oxygenating plants like hornwort.

If fish die do not replace them immediately. Do a water change – no more than 25%. Watch the other fish for signs of respiratory distress (coming to the surface to gulp air). You may have too many fish for your bacterial population.

Finally, keep a list of what fish you have in your aquarium.

Pet store owners hear this all the time:

“I want a fish that will go with what I have at home.”

“What do you have?”

“I don’t know – it’s about this big and looks kind of like that fish there, only the tail is different.”

When you buy a fish, ask for the name of it and write it down. Then you can say “I have five tiger barbs and three serpae tetras”, and your pet store owner will love you, guaranteed. He or she will also be able to help you choose something that won’t eat what you have, or be eaten or bullied by it.

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