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Salmon in the Classroom Resource Menu Bar

Tank Problems

Feeding Problems

Cloudy Water

Dying Fish

How to Do A Complete Gravel Wash

This job will take 1-3 hours depending on how much help you get. It is the last resort when conditions in a closed system tank have gotten out of control. Generally there are two ways this can happen.

Gradual mess: The tank has gradually gotten so messy from over-feeding, under-cleaning, and overcrowding that moderate maintenance (2-3 buckets of water twice a week) is not adequate to keep the pH above 6.4 and the ammonia level at zero.

Catastrophic mess: Someone has overfed the fish so drastically that the water is cloudy and smelly and the fish are in visible distress. Unless you act fast, they will die.

There are two ways to address the problem:

  1. Print out the checklist of tasks.
    Assign tasks to various people.
    Check off tasks as they are done.

  2. Print out the checklist of tasks.
    Give a martyred groan.
    Get to work.
    Check off tasks as they are done.
Here is the checklist of tasks:

First take the fish out

1. Fill a five gallon bucket 1/2 full of dirty tank water. Fill it the rest of the way with clean tap water. Mixing old and new water is necessary to avoid injuring the fish by changing their water conditions too fast. If you have a bucket to spare, prepare two buckets of water so you can divide the fish between them.

2. Remember to add the appropriate amount of Shieldex to dechlorinate the tap water.

3. Aerate the water in the bucket with the tank pumps and airstones. Check to be sure the airstones are putting out a good stream of bubbles. If they aren't bubbling vigorously, put on fresh airstones. If you don't have replacement airstones, pull the old airstones off and run air through the bare tubing. Do not put salmon in a bucket without good aeration or they will suffocate!

NOTE: If your fish are very young or weak, put the bubbling airstones just below the surface of the water so that they will not generate so strong a current in the bucket.

4. Net the fish and put them in the bucket. Set the bucket in a cool place while you deal with the tank.

Clean the tank


1. Unplug all electrical aquarium equipment except for the pumps aerating the bucket of fish.

2. Drain the tank completely.

3. Rinse tank with clean tap water. Wipe the inside with a clean paper towel.

4. Disassemble, rinse, and wipe the filters, tubing, thermometer, etc. Rinse the sponges and oyster shells in running tap water.

5. Replace the airstones if they are clogged.

Clean the gravel

1. Take out about two cupfuls of dirty gravel and set it aside. Because cleaning gravel with chlorinated tap water will kill most of your friendly waste-eating bacteria, it is very important to save some dirty gravel with bacteria in it to re-colonize your tank.

2. Put the rest of the dirty gravel in two buckets.

3. Take the two buckets of gravel outside and set them on the lawn or sidewalk. Jam a garden hose deep into the gravel of one bucket and turn the water on full blast. Stir and rinse the gravel vigorously until the water runs clear. Repeat for the other bucket of gravel.

Reassemble the tank

1. Reassemble all the tank equipment and put it back as it was in the tank.

2. Put the clean gravel back in. Put the two cups of dirty gravel back in.

3. Refill the tank with cold tap water. Remember to add Shieldex to dechlorinate the water!

4. Plug in all your equipment. Check to be sure everything is still working properly.

Prepare to put the fish back

1. Take out about half of the water in the bucket. Replace it with the new, clean aquarium water. Give the fish about 15 minutes to begin to get used to this new water.

2. Net the fish and return them gently to the tank.

3. Darken the tank and leave the fish alone for awhile to calm down.

Follow-up care for your injured tank

Washing with chlorinated tap water killed or removed most of the bacteria in your gravel. It will take several months for the waste-eating bacteria population in your undergravel filter to stabilize and be able to clean water efficiently. In practical terms, this means that for the next year, you must be especially conscientious about feeding the fish properly, keeping the tank clean, and monitoring your water quality by taking pH and ammonia readings regularly.

If you fail to do this, the water quality in your tank will deteriorate even faster than before and you will have to do yet another gravel wash. UGH!!

Salmon in the Classroom Home Page
Getting Started
Care and
The Field Trip
Closed Tank | Open Tank | Semi-open Tank | The Salmon
Closed Tank Timeline | Open Tank Timeline | Semi-open Tank Timeline
Closed Tank Feeding | Open Tank Feeding | Semi-open Tank Feeding
Planning | Background Info | Worksheets | Leader worksheet key
Tank | Feeding | Cloudy water | Dying fish | Gravel wash
Funding | Permits | Glossary | Locating Special Equipment| Additional Resource 

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