“I have an aquarium but it’s so much trouble that I’m ready to take it down.”

 “My fish keep getting sick and dying, what am I doing wrong?”

 “How do you get rid of all of this algae?”

“My tank stays cloudy and dirty!  How do you keep yours so clean?


Robotically, I start asking a list of questions to help identify the problem.

What size tank do you have?

What type of filter?

How long has it been set up and running?

How many fish do you have?

When did you add new fish?

How much do you feed?

How often do you do a water change?

Have you tested the water?


I’m Larry and I’ve owned an aquarium maintenance company called Aquatic Designs for over 20 years.  In my time of maintaining customer’s aquariums, managing the fish department in a big box store and owning my own aquarium store, I feel like I have heard of or encountered just about every problem imaginable with an aquarium!

Almost always, when I am talking to someone who is having a problem with an aquarium, the root of it seems to come from one or more of these three things:


Adding Fish Improperly

Not Cleaning Correctly

Since I can’t be there to ask you those questions, I will address each one of these issues.  Since probably 90% of all problems with an aquarium revolve around these things, you may find the source of your problem.

These mistakes can be made in both freshwater and saltwater aquariums alike.

In this article you will discover that keeping an aquarium should be fairly simple….taking only a few minutes per month on routine maintenance and spending very little money on chemicals and supplies.

Mistake #1


If you think that you are overfeeding…….you probably are.


If you think that you are not overfeeding…….you probably are.

Overfeeding is likely the #1 cause of problems in an aquarium.  People tend to feed their fish more than they actually need.  Fish will instinctively keep eating – even if they don’t need it – since they don’t know when their next meal will come.  Excessive eating normally doesn’t harm the fish but it’s the food that is left over and what comes out of the fish later that does.

Why is Overfeeding Bad?

After feeding, uneaten food begins to decay and fish excrete waste and ammonia. If they’re overfed, these wastes will build up at a faster pace.  They will begin to build up to levels that can be toxic to fish causing disease and death.  Overfeeding can also cause algae blooms, cloudy water and that “fishy” smell.  Think of it as the same as smoking a carton of cigarettes in an old, glass telephone booth without ventilation.

How do I know if I’m overfeeding?

Here are a few symptoms that may indicate that you are overfeeding:

Water tests show that Ammonia and/or Nitrite are present in an established aquarium that is more than 6 weeks old

The water has a yellow / brown tint

Excessive green, red or black algae

Uneaten food or white fungus like particles on the bottom of the tank

Filter pads or sponges getting dirty really fast within a few days instead of a few weeks

Nitrate is at a high level

pH keeps dropping due to acids produced by excessive fish waste

Fishy smell

Some of these symptoms can also be an indicator of not enough water being changed during cleaning.

How much should I feed?

I try to use the gauge of a 1/4” square piece of flake food – per 1” size fish – once per day.  Obviously, I don’t measure this out for every fish, in every tank, every day.  Do this once on a piece of paper so you can get an idea of how much food you should be feeding your fish.  Lay the paper on a table and arrange that amount of food for each fish in the tank.  If you have fish that eat pellet or another type of food, a good gauge is to arrange enough food equal to the size of its eye.

This exercise should get you within the ball park and you may find that you have been feeding too much. You will soon learn how to monitor your fish and your aquarium to make sure that you are feeding the right amount.

More Info Hydor Automatic Fish Feeder

How often should I feed?

It doesn’t matter whether you feed once or twice per day.  If you feed twice, just split up the amount of food that you would have fed once.

If you have to go out of town for a couple of days then don’t worry about feeding.  Fish can go for several days without eating and be fine…as long as they have been fed up to that point.  If you leave town for a week, I suggest buying an automatic fish feeder instead of having a neighbor feed your fish.  I’ve had plenty of people come into my store to buy replacement fish that they killed while they were feeding their neighbor’s tank.


Feeding correctly will lower the amount of waste in the water thus lowering the amount of stress, disease and death of fish.  It will also reduce algae blooms and the frequency of water changes and cleaning.


In order to fully understand the next two mistakes, you need to have a basic understanding of how an aquarium naturally works.  This will help greatly in how you approach adding new fish and proper cleaning.

How an Aquarium Naturally Works

An aquarium has a natural way to process fish wastes into less harmful substances. This process is called Biological Filtration.  Uneaten food and fish waste will begin to break down by good bacteria into other substances.  The aquarium’s ability to process this waste depends on how long the aquarium has been set up & running (with fish) and how you clean it.

If your aquarium is new (6 weeks old or less)….there may not be enough good bacteria established to process all of the ammonia and nitrite that is building up. High levels of ammonia and nitrite will cause stress on fish which in turn cause a lowered immune system, disease and death.  It can take up to 6 weeks for these bacteria to build up to a high enough level to process these wastes.

If your aquarium is established (more than 6 weeks)….the last substance (nitrate) will begin to build up. If it is allowed to build to high levels, it can become food for algae.  This is usually the source of prolific algae blooms in an aquarium.  High nitrate levels can also be stressful on fish causing disease and death.

If your aquarium is established….but you have removed and cleaned all of the gravel, filter and decorations, you may have killed the good bacteria. The aquarium is now considered “new” and has to cycle again. You may now have elevated ammonia and nitrite levels as the bacteria reestablish themselves.

♦ If your aquarium is new …. you can speed up the bacteria cycling process by adding bottled bacteria to the aquarium.  This is the good bacteria that is used for biological filtration concentrated in a liquid.  This will help to kick start the aquarium to keep ammonia and nitrite levels down.

More Info Seachem Stability Fish Tank Stabilizer


Determine where your aquarium is at in the establishment of these good bacteria. Is it “new” or is it “established”?  This will determine how you handle the next two mistakes.

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Mistake #2

Adding fish improperly

Another major cause of fish disease and death is from not adding fish properly.  In a new aquarium, it is usually from adding too many fish too fast.  In an established aquarium, it can be from adding fish to water that hasn’t been changed in a while and contains high levels of waste such as nitrate.

New Aquarium

When setting up a new aquarium, no bacteria are present. After adding the first fish, ammonia begins to build up. Bacteria enter the water and begin to multiply, transforming ammonia to nitrite, then to nitrate. If you add several fish at first, a lot of ammonia will build up. If too much ammonia builds up, your fish will get stressed, sick, and could die. It is best to add only a few fish at first, keep the ammonia level low and allow the bacteria time to build up. It may take four to six weeks for the ammonia and nitrite levels to fall to “0”.

How many fish should I add?

Start out with very few, about two regular size fish per ten gallons of water. This doesn’t sound like a lot of fish, but it will save you a lot of headaches in the future. After the ammonia and nitrite levels fall to “0”, then you may add a few more fish.

Never, never, never add new fish to an aquarium if ammonia and nitrite are present!

If you have already added a lot of fish and the aquarium is new, you can add bottled bacteria to help kick start the establishment process.  Reduce feeding to once every other day and cut the amount in half.  This will reduce the ammonia levels as bacteria build up.  It is better for your fish to be a little hungry than to have ammonia burning their body.

♦♦Note about water changes in new aquariums♦♦ 

I would not do a water change in a new aquarium 6 weeks old or less unless the ammonia, nitrite or nitrate levels are very high.  If you do, then you are removing the good bacteria that are trying to get established and settled down into the rocks and filter.  If they are in safe ranges, just cut feeding down and let the aquarium finish cycling.

Established Aquarium

Test the water before going to the fish store.  If nitrate levels are high, do a water change before adding new fish then test the water again.  You may add a few more fish than a new aquarium but I would limit it to two to four regular size fish per ten gallons.  There are only enough bacteria present to process the waste from the current load of fish.  If you add more fish, more bacteria will have to grow.  I would also cut feeding in half then slowly build it back up over the next two weeks.  This will keep ammonia levels low as the bacteria grow.


Many pet stores have been falsely accused of selling sick fish. The fish were probably healthy when they left the store, but they were put into aquariums that have not had water changes in months or they were put in with too many other new fish and were victims of high ammonia and nitrite levels.

Changing this will greatly reduce the headaches from sick and dying fish.  I couldn’t even tell you the last time I had to medicate a tank for ich from sick fish!

Mistake #3

Not Cleaning Correctly

Over time, wastes build up in the water, even though the water is crystal clear.  One of the ways to remove and dilute these wastes in an aquarium is through partial water changes. The amount of water that needs to be changed depends on how many and how large the fish are in an aquarium, but a general amount would be 25% to 30% per month. Replacing water that has evaporated does not constitute a water change.  The dissolved wastes do not evaporate.

How do I do it?

When doing a water change, you should use a device that will vacuum the gravel.  These are readily available at most fish stores.  This will pull out fish waste and uneaten food without harming the good bacteria that is growing on the gravel.  When about 25% to 30% of the water is gone, add new water to finish filling the aquarium. If you think you need to take more water out, then do so. If you have skipped a month or more, then increase the amount changed.  The fish can stay in the tank as you do this.

When adding new water, get it as close to the temperature of the water in the aquarium as possible. If you are not able to get the water close to the aquarium temperature, change a smaller amount of water so it won’t shock the fish.  If you are on a municipal water system, add a chlorine remover as soon as you start to refill the tank. If it is a saltwater aquarium, mix the salt with the water in a separate container and allow it to dissolve thoroughly before adding it to the tank.

More info Python No Spill Clean and Fill

What not to do

It is actually possible to overclean an aquarium.  You should never completely empty and clean out an aquarium unless all of the fish are gone and you want to start over.  When you do this, you can harm or kill the good bacteria that are growing in the gravel, filter and decorations.

More Info Mag-Float Glass Aquarium Cleaner


When you control feeding and fish load, you will find that the aquarium will stay cleaner and will have to be maintained less often.  Fish will be less stressed which in turn will keep disease and death to a minimum.

Larry has been in the aquarium industry for 20+ years doing everything from retail, maintenance, publishing, commercial repair and consulting. He lives with his family on their 10 acre "farm" .... which is just a code word for "petting zoo". His "happy place" is sitting on his John Deere tractor. Follow his maintenance business on Instagram @larry_thefishguy