How to Save a Sick Aquarium

Everything was fine last night. You fed the fish, went to bed, and woke up to ... disaster. The inhabitants of your freshwater tank are either dead, swimming sluggishly or hovering near the surface, gasping for breath. You see some ragged fins on your shark, maybe patches of fungus-looking stuff on a platy. What happened? Before you rush to the pet store to buy medicine, realize that when a freshwater tank "goes bad" all at once, it's most likely because the fish waste products have overtaken the fresh water. You can fix that.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Seasoned water (or instant water conditioner)
• Siphoning device to clean gravel
• Water bucket
• New filter inserts
• Carbon sachets

How to Save a Sick Aquarium

1. Immediately add as much fresh, conditioned, temperature-appropriate water as you can without overflowing the tank. If you don't have conditioned water on hand, use water conditioning drops and use a meat or candy thermometer to bring tap water to the same temperature as the tank water.

2. Use the siphon to pull dirty water from the bottom of the tank, letting it drain into a water bucket. The material poisoning your tank is on the bottom, either under the under-gravel plastic plate (if you have one) or nestled in the gravel itself. Move the siphon frequently, nestling it down into the gravel until you see the muddy water coming through the hose. As soon as you siphon out half a gallon of dirty water, add half a gallon of clean (conditioned, temperature-correct) water. This will change the nitrogen balance in your tank immediately. If adding new water makes your aquarium heater go on, you've made it a little too cool; allow several minutes for the heater to warm up the new water before continuing. Siphon out as much waste as you can.

3. Change out all filters. It's not necessary to remove, dissemble and scrub the filters. Just get the filtered water moving through fresh charcoal as soon as possible.

4. Drop in carbon sachets, which are little fabric bags of activated charcoal sold in pet stores as "instant tank fresheners." They will help sweeten the water, although they can't overcome the waste, so they won't take the place of siphoning.

5. Take stock of your tank. Remove any dead fish. Turn on the tank lights and inspect the survivors. Fish with ragged fins will probably recover. Fish showing patches of fuzzy, fungus-looking stuff might also recover, but watch them closely. Don't feed the fish. If most of your fish look sick, buy fish tank antibiotics to treat bacterial infections and treat the whole tank. But be aware that the medicine is also stressful to the fish, so give them a full day to recover in the fresh water before you dose the tank.

6. Once your tank has stabilized again--which should happen within 24 hours--feed the fish. Commit to a regular schedule of siphoning/replacing water so this never happens again. If your tank is overcrowded, consider giving away extra fish or setting up a new living space for them.

Tips & Warnings

• You should always have a gallon container filled with tap water on hand. Store it near the tank so it's the same temperature as the tank water. This can save your fish if, for example, the tank breaks.
• If you have mostly top-feeding fish, buy fish food that floats. Less of it will get lost in the gravel.
• Consider adding a bottom-feeding fish or two, such as a plecostomus or cory, or a snail to help break down uneaten food.
• Don't overcrowd your tank. The "one inch of fish per gallon" rule is an upper limit; don't push it. If you find yourself with too many fish (if they start to multiply on their own, for example) you'll have to add additional filtration.
• Goldfish are among the biggest eaters/waste producers in the freshwater hobby fish world. Don't keep more than 1/2 inch of goldfish per gallon, and be ready to do some extra siphoning and filtering as they grow--which they will.