Introduction: Dirty Tank? Let's Clean It Up!

Picture of Dirty Tank? Let's Clean It Up!

It starts out slowly.  The first day you get your fish, your tank is sparkling clean.  A few weeks later you notice the tank is looking a little cloudy.  You ignore it.  Two more weeks go by and your fish tank is starting to look like mine did.  This can be very overwhelming for a new fish owner.  Don't sweat it, I've got you covered.  Just follow this step-by-step instructable, and before your fish know what's happened they'll have a fresh, clean tank.

Step 1: Background

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Before beginning the tank cleaning process it's important to note a few things first.  This instructable is designed for small to medium sized tanks (5-20 gallons). The instructable is also designed for freshwater tropical fish, meaning that the water temperature is meant to stay in the mid 70's.  The tank that I am demonstrating on is a rare case.  It is much dirtier than it should ever be.  Most cleanings should not wait until the tank is this dirty.  In fact, every other week you should plan on cleaning your tank.

Step 2: Materials

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Aquarium salt.
Water conditioner.
Fish net.
Temporary fish tank.
Water siphon.
Clean container.
Large bucket for waste water.

Step 3: Unplug Electrical Devices

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The first thing you will need to do is unplug all devices such as the aerator, filter, and heater.  I suggest leaving the hood lights plugged in and simply setting the hood behind the tank to help illuminate the tank.

Step 4: Remove Decor & Fish

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Begin removing all decorations and electrical devices from the tank.  Be carefully not to harm the fish in doing so.  Once the decor is removed, you can next remove the fish.  Fill your temporary fish tank with some of the original fish tank water.  It is important to use the current tank water when filling the temporary tank as this will provide less environmental stress on the fish.  Gently transfer all fish from the current tank to the temporary tank using the fish net.  Be careful not to allow the fish to jump from the temporary tank.  I recommend having a lid cover the temporary tank.

Step 5: Vacuum the Gravel

Picture of Vacuum the Gravel

Now, you can begin the actual cleaning process.  Use the water siphon to remove the dirty water and also vacuum debris from the gravel.  The easiest way to start a siphon is to fill the vacuum end with water and then move the siphon quickly up and down several times.  Make sure you have a large enough container in place to catch the water as you siphon it out.  It is important to vacuum through all the gravel with the water siphon to remove fish waste and leftover food.  You shouldn't have any problems with the water siphon vacuuming up the gravel as it will be too heavy.  Remember to remove no more than 75% of the water from the tank. This will ensure that you do not remove all the vital bacteria that your fish need to survive.  In fact, a typical clean should only require you to remove between 25% and 50% of the original water.

Step 6: Clean the Glass & Decor

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Wipe down the inside of the glass using either a clean rag or paper towel.  Do not use any cleaning chemicals such as soap to help clean the glass, as this can harm your fish.  If you own a plecostomus, I suggest leaving one of the sides of the glass untouched in order to preserve some algae for the pleco to feed on.  You may also wipe down the outside of the fish tank if needed.  Be sure to rinse off any decor items as well by simply running water over them.

Step 7: Refill the Tank

Picture of Refill the Tank

You are now ready to refill the tank.  Begin by replacing all decor items including the heater and aerator.  Do not plug these items back in yet.  Grab your clean container and begin filling the tank with tap water. Try to refill the tank with water as close to the same temperature the tank initially had. You will want to fill the tank about 90% full to allow room for the aquarium salt, water conditioner, and fish. You may now plug in all electrical devices.

Step 8: Add Salt & Conditioner

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Now that you have gotten all you water added and heater plugged back in, you are ready to add the aquarium salt and water conditioner.  Read the instructions carefully for both chemicals, and add the recommended amounts of each into the tank.  Allow the tank to sit for 15-20 minutes while the chemicals diffuse and the water temperature balances out.

Step 9: Return Fish and Enjoy!

Picture of Return Fish and Enjoy!

You may now return your fish to their new and now clean home.   I recommend cleaning your tank every other week.  In doing so, a 25% to 50% water change should be fine.  You should also change the filter every other week.  Be sure to stagger the interval between your filter change and water change in order to preserve the helpful bacteria and to lessen the shock on your fish.

Step 10: Important Tips & Warnings

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1. Make sure your new tank water is the same temperature as the water the fish are currently in. This will reduce the shock on the fish.
2. Avoid leaving your fish in the temporary tank for more than 30 minutes.  Eventually they will run out of oxygen if left for too long without an aerator.
3. Avoid frequent large water changes.  Typically you should only change between 25% and 50% of the water.
4. Never use any type of soap products to clean the tank.  Soap has harmful chemicals that may kill your fish.
5. Never try to move a full fish tank.  They are much heavier than they appear, and this will most likely end badly for you and your fish.


feeshy (author)2010-03-19

If the tank looks like that, there's definitely something wrong...

Firstly, changing the filter media? Very bad plan. That's probably got a good deal to do with why the water is so cloudy. The filter media is what houses the bacteria required to remove the ammonia and nitrite produced, only a very tiny percentage occupy the substrate and water.

Salt is completely unnessecary for a freshwater tank, hence the name. Fish don't gain anything from it, you're just wasting your money.

There's no need to remove the fish; that's just going to cause stress that isn't needed. General reccomended water change regime is 25% once a week. Dechlorinate the water in the bucket before you put it back in the tank. However, if the tank is in the process of cycling with fish, then more frequently is definitely a good idea.

thebriguy (author)feeshy2010-04-15

feeshy, I disagree with your first 2 points;

1) 25% water change monthly - more often if you have a problem or imbalance.
2)Salt is good - I've used it in my tanks. It color enhances the fish and is good to use if there is a proplem like ick.
I agree with your last statement - there is no need to remove the fish. The only time I may remove one is if I move it to a hospital tank for treatment - so I don't dose the entire tank.

I believe in keeping things as simple as possible when keeping fish. If it's too much work it is not fun, and the maintenance doesn't get done.

In my years of fish keeping and reading about it I've noticed many styles of keeping the tanks. So, if your having success keep doing what your doing!

WesleyG24 (author)thebriguy2016-11-19

It's 7 years but there's been some changes/upgrades for the better. I completely agree with you.

LaKeishaB (author)2016-02-29

I have a 30 gal fish tank every time I clean my fish get sick don't know what I did wrong a few day later white stuff is on the fish I lost two of my three fish I am also having high ammonia problem. can any one help me

AyeEvan (author)LaKeishaB2016-08-18

Your fick has the ick u can got to a petco to get ick medicine for ur fish

CouinE (author)LaKeishaB2016-03-07

PS. you let the tank filter and run for a while before you put the fish back in

CouinE (author)LaKeishaB2016-03-07

hey, do you give the tank any time to adjust when you add the water conditioner? Also, just get a water neutralizer and adjuster tablets for your tank. If that doesn't work, it is the temperature of the tank.

RachelP69 (author)2016-07-11

Hi everyone. I've never had a fish in my life. Bought a Betta and a 5 gallon tank. Unfortunately, before I began reading instructions on water/ph etc. I cleaned out the tank AND gravel with dish soap. Now it's Meyers dish soap which you can basically eat (I'm exaggerating), but still soap nonetheless.


My little Betta is still in the little bowl from the pet store. How long can it stay in the bowl?

AshishT36 (author)2016-07-08

think its sill dirty

rdavis56 (author)2014-05-16

I have a 55 gal fish tank! I some how killed 3 batches of fish and now I'm on my 4th I don't get it my fish tank is beautiful and spotless but my fish are still dieing. I'm changing the filters when needed I add the conditioners, I don't know what's going on or why! I have 2 plecos,did have 4 baby cat fish and 2 angel fish and 2 kissie fish now I only have 1 angel fish 0 cat fish 1 kissie fish and 2 plecos.I feed them when needed and know not to over feed them and I also got my water tested and the pet store said that the water was fine for my fish..they have some kind of white stuff on them and I don't know if it's algae or not but I was told that the tank needs some algae because I have plecos. If any body has any answers please's getting very expensive to keep this tank.

Mikeyb223 (author)rdavis562016-01-18

Hey bud, the white spots on your fish is more than likely ick, a very common disease fish can get. And what i would recommend is putting the remaining fish you have in a small holding tank for a few days while you clean and disinfevt the tank you currently have. A great way to clean it without chemicals is with 20 mule team borax. Its in the laundry aisle at the supermarket, and its a naturally occuring mineral (its actually a crystal that is ground up, which has amazing properties of healing, disinfecting, and cleaning. So once your tank is clean you might wanna think about replacing the sand or gravel as well but if you can't or don't want to you're gonna wanna tell your tank with distilled water. Tap water nowadays, and even purified water, and in some cases (walmart) even the distilled water has flouride in it, which is poisonus to every living organsim on earth. I'll guarantee thats what your problem is. You can make a home distiller for about 20 bucks and turn water from your hose into pure H2O! I would suggest investing in that cuz buying distilled water by the gallon can get quite expensive depending on your tank size. And just remember that outting in fresh water in a clean tank means that there will be no bacteria in the water that the fish need to servive, so ask your local pet store for a gallon or so of their tank water cuz youre you're starting up a new tank. And something i tried that worked better than anything i could have ever imagined to get rid of ick without chemicals, was just a tabelspoon of colloidal silver, a ruby that cost $2.00 from a gemstone store, and a clear quartz crystal. My Moms friend suggested it i told her she was crazy, she took offense came over to my house amd put it in herself, and within 20 minutes the ick was gone. Which up until then i couldnt get rid of it for the life of me. (Shoulder shrug) Idk how or why but it worked.

BrandonC57 (author)rdavis562016-01-08

I'm assuming that the issue was resolved by now, or you got rid of the tank... but for other readers that may be having trouble with similar issues. Please use the forums and aquarium hobbyist websites to help you determine what fish will work well together in a tank. was the one that I learned so much from when I started keeping fish in high school. 10 years later and I'm still a member helping newcomers to the hobby.

As for the fish, they are uncompatible to live together, and if there is not enough algae in the tank for plecos, you can feed them leafy greens, zucchini, or other veggies (do your research first though) until the tank gets a little more healthy and green! There are also algae tablets that you can buy to feed them, but they are pricey!

PujaD (author)rdavis562015-05-10

it's probably not the tank

Caleb McKelvey (author)rdavis562015-02-05

I work at pet smart the thing wrong is that u cant have other fish in the same tank same thing happend to me and they kill each other the catfish is a bottom feeder and wont survive im sorry

CandaceM23 (author)rdavis562015-02-04

Your fish have ick or ich it's potentially deadly but you can save them... There's lots of info online... Good luck...

Jawatech (author)rdavis562014-09-14

rdavis56 Sounds like you have a bad case of Ich. Most likey from your petstore.


Londov7 (author)2015-10-01

I have a 55 gal tank and I can't figure out why I keep having my fish die on me! I started with 2 dalmation mollies, 2 red velvet wags, 2 guppies, 1 algae eater and 11 neon tetra fish... All of them are small with plenty of room. My male wag died the very next day so I went and bought another one and he died after 4 days, now I have 3 or 4 tetras that are going belly up! Checked the PH levels and they are fine, filter is working, bubble machine is on low to medium and I've got 2 live plants in the tank. I don't see anything on the fish and I take the dead ones out right away. What's going on? Any suggestions?

BrandonC57 (author)Londov72016-01-08

Did you let the tank cycle properly before adding fish? Sometimes people don't realize that a fish tank is actually an ecosystem and think "add water and fish" but in reality it takes a little more time to make something that will thrive and be beautiful.

If the tank has been set up longer, then it could be any number of other things. Without more explicit information we can't really determine what's going on in your tank.

thruthefield (author)Londov72015-11-04

Put the dalmation mollies in a seperate tank for a bit and see what happens. I had one that killed off nearly my entire stock. If the fins look ragged or are gone by time you take the dead fish out you have an aggressive fin nipper on your hands.

apadilla101 (author)Londov72015-10-16

Check with the sales associates ! It also depends where you are buying your fish from. One of the main reasons of fish deaths, are because people commonly bunch different kinds of fish together ! For example, many people put common goldfish with tropical fish. Believe it or not, goldfish aren't considered tropical fish. Goldfish are used to being in the range from 50 to around 60 degrees Fahrenheit in fresh water, where other fish survive in being in higher temperatures ( tropical fish ). Like guppies, their range is around the tropical range as well, ( 75-88*f ). Your fish do seem to be in the tropical fish so it might not be the temperature. Have you noticed any fighting ? or any heavy objects ? Fish tend to " race " around and get hurt while doing so which may cause internal damage to the fish. Some fish just dont get along.

BrandonC57 (author)2016-01-08

While this is a great start, this is not the way to properly clean a healthy aquarium.

First thing is, you do not need to remove the fish and decorations from the tank to clean it. Rather, you should only remove about 25-50% of the water while you are doing your gravel vacuum.

Before you add any water back into the tank, you should add the water conditioner/de-chlorinator and try to get it to about the same temperature as that in the tank by playing with the hot/cold water taps from where you are filling it. If you're using a garden spigot, add hot water from a tea kettle or pot to warm it up.

If you're having problems with your fish and tanks, i suggest joining a forum. Communities of long term hobbyists, professionals, and new comers alike to help each other out. I recommend as a good beginners forum.

EvelynA9 (author)2015-12-31

I need Help on how 2 Clean the filter .. u didn't Show it here .. ? ?

So what you have to go is take the dominant filter out and take some of the tank water and put into a bucket and clean the filter in the water until all of the food and poop is out of the dominant filter and put it right back into the filter and you are good to go for another couple weeks but after a few months you might have to replace the dominant filter because it will tear and fall apart. Good Luck!!

a98765 (author)2015-05-24

water conditioner/dehlorinator should be added to the new water before refilling the tank, otherwise you'll harm the bacteria.

PujaD (author)2015-05-10

lynette.bost (author)2015-02-08

My 1. Mistake was cleaning the gravel to well, cause large amount of hidden gas into the tank ,which in turn killed my fish, so have had to start over!

tucker5455 (author)2014-12-28

Thank you soooo much I just got a 20 gallon tank completely free form my grandmother and it was very dusty in her house so I used the methods you used to clean it. Thank you I will post a pic when it is completely set up in about 2 weeks.

Azze01 (author)2014-10-06

My 5 cts: Find someone with a well-running, healthy fish tank and ask him to let you have the filter material he's willing to dispose of. Get it right out of the filter and squeeze it deftly in your fish tank. Sounds disgusting? It is, believe me! Plus you will gag over the mess this act creates in your tank. But believe it or not, this will import the good bacteria into your tank that you need to run it properly.

Cleaning too much is a dreadful thing to do to a fish tank. One has to distinguish between mechanical cleaning an biological cleaning, which definitely is NOT the same thing. Most people think of the aquarium filter to be something like a vacuum cleaner in the house. Take away the dirt and everything is fine? Well, this is wrong. While too much detritus (decaying plants, animals etc.) is a bioburden to the tank, too little of it is a disaster, as it is the home for a living bacteria colony in your tank. plus, this detritus has been found to have a stabilizing effect on the ph value as it has some ion exchanging capacities. But that's another story.

Base line is that too much mechanical cleaning will kill your bacteria, which in this case is NOT something you want to aim for. These bacteria can be found on every surface (gravel, plants, wood...) in the tank and help to convert ammonia via nitrite into nitrate. Thus, your filter is not there to swallow the dirt but to increase the physical surface for the bacteria. Once the bacteria are settled and active, filters with a slow water flow and high filter area are basically maintenance free. No need to clean them every second week. Leave them alone and let them do their work.

When doing water changes, keep in mind, that to dilute some substance in the tank to half the value, you have to exchange 50% of the water. That said, think about the effectiveness of a mere 10% water exchange. There is no danger of washing out the desired bacteria as most of them love to settle on substrate and don't float in open water. So if you go and exchange water, you'll lose only few of them.

My advise: Take generous water exchanges, leave the filter alone and stop scrubbing down the decoration. Oh, and put some real plants in there. Not only will it look much better, they will also take care of a good part of the waste products of your fish (nitrate, at the end of the day).

Good luck!

SIRJAMES09 (author)2011-07-04

I have raised fish for YEARS and NEVER,EVER removed any water....

on a 55 gallon tank, I had 2 bio filters & 1 particulate filter. never once did I have to remove any water in over 8 YEARS.

Now, I'm not saying I'm right & you're wrong, I'm just saying that it doesn't make sense to me.

not bad tho. you did pretty good. 8-)

zwhenry (author)SIRJAMES092014-06-17

You must have either huge overpowered filters or extremely hardy fish.

colorfish (author)SIRJAMES092011-07-08

wow. that is very cool. what is the brand of your filter?

zwhenry (author)2014-06-17

You shouldn't have 2 (let alone 1) oscars in that tiny tank. To house 1 oscar, you should at least have a 55 gallon, if not larger. They should grow at a rate of about 1" per month, but the growth will be heavily stunted if you don't allow them the proper space. These fish can get to be up to 18" long, and thus need a very large amount of space.

bubba j (author)2014-04-22

you wouldn't have had this problem if you would have cycled your tank to begin with, and your gravel bed is too deep, waste will settle at the very bottom and anarobic bacteria will develop, and they can poison your tank.

I'm gonna try this i think!

gonzo93 (author)2014-02-18

Thanks! It was really helpful. I finally got my tank clean the way it should be.

infernisdiem (author)2013-11-09

i have a 55g tank that i set up in feburary, and haven't changed the water in since, every once and a while I will top it off, and once in a great while i take the filters out to rinse off, haven't had an issue with my fish doing this. Something that i found to help with keeping the tank clear, is not to over feed the fish, and possibly put a slightly stonger filter in your tank.

spdoug123 (author)2012-12-02

An Albino Tiger Oscar and a Red Tiger Oscar make waaay more poop than that tiny tank can handle. Plus, they won't be able to live there in adulthood.

Ramming (author)spdoug1232013-07-30

Yes I had four Red Tiger Oscars and I had them in around 270 gallons. I seem to remember that you need around 70-72 gallons to keep a full grown specimen. I had a massive pump system and a defoaming tank that kept the protein level down and filtered the water efficiently.

spdoug123 (author)2012-12-02

Tap water? Maybe if you let it sit in a bucket for a few hours first...

Raven68 (author)2012-01-20

I just got a 55 gal tank from a guy. It smells & has dirty water rings. I'm new to this,but I want to give it a good cleaning before I decide what to put in it. The guy told me to use comet cleanser & detergent. Any suggestions?

knexfreak32 (author)Raven682012-08-14

A little bit of white vinegar on a sponge rubbed along the water lines should work.

revpatrickchand (author)Raven682012-02-22

Oh please dont use any detergents AT ALL! Yes some will say the nitrogen cycle will take care of that issue in due time and I will agree if everyone has the time to wait. The use of detergents will cause great chemical instability in the tank affecting all inhabitants. Besides death of your specimens unruley algae blooms will happen. That silicone bead on the sides of the tank surprisingly hide "footprints" of alot of things toxic. Not to scare you or anyone else it is somewhat simple to clean up an old glass tank with history lines.
Of course use an area that can accomdate alot of splashing. Hose down the aquarium, if you need some courseness for cleaning use a little bit of regular table salt. If the rings persist use a razor to "shave" off the film. once you are satisfied rinse. No detergents please. Please remember this is for glass only!
After 25 years in the marine tank husbandry and manufacturing I may have learned something.
Rock On!

steel wool would also be a great help in removing those rings!

suzo77 (author)2012-05-16

What do you do here if there are tiny baby fish in the tank?

toonutz (author)2011-11-29

And always remember to let your heater cool down (if it's glass) before taking it out of the tank otherwise it'll crack. It gets to be an expensive mistake!Otherwise, good instructable!:)

beltrankevin (author)2011-05-24

i would recomend you a biofilter that doesn't kil or avsorbe any fich

gapak (author)2011-03-26

Just a 'few' comments...

- For larger aquaria it's better to clean them every two weeks.
- About the waterconditioner/aquasafe and similar products: Before you buy one of these, make sure you really need it. There are many countries where the quality of tap water is good enough. In that case it's better not to use this product in stead of using them. Sellers won't tell you this...
- Never go longer then 2 weeks without any water changes.
- When you have this problem dirty cloudy water it can mean two things:
1. Algae, solution: keeping real plants in your aquarium.
2. Dead bacteria, solution: make sure your filter is on 24/7. When you have an internal filter you'll have to shut it down during water changes. Prevent the filter from being down more then 20 minutes. To achieve this you'll have to make sure the new water is ready in a few buckets before starting to empty the aquarium. (this is what you did wrong, jtvreeland) Never change more then 30% of the water. In fact: if water values are good, only change 10% of the water!
It's also very important that your aquarium isn't to small for the fish. The length of the aquarium has to be 10 times the length of the adult fish. (exept fish who don't move a lot like ancistrus species) Make sure also you don't put all the fish at once in a new aquarium. After the first week only 3 who belong in the upper water level. A week later you start working on the lower water level for 2 or 3 weeks. Another week later you start again adding fish who belong in the upper water level. Fish who belong in the middle water level enter the aquarium last (and at once).
- Never clean the entire filter (in the same time). Also never change the water and clean the filter at the same time!
- Rules like 10 gal per inch of fish don't make sense. The lenght of the fish doesn't tell anything about how polluting it is. Just follow the other advises and you can add as many fish as you want. (ok, not as many fish as you want but you'll be happy long before you reach the real maximum of what your aquarium can take.)
- Only use the fish net if you really have to (and not to get your fish in another tank which is totally unnecessary), the risk of damaging the fish is to big to do it when it's not really necessary.
- Get two species who clean the tank for you if your not able yourself. I advice two species of a different kind like an ancistrus or pleco and a corydoras. Taking two species prevent them from being lazy because then there's a competition between them. If your aquarium is clean (no algae on the windows) you'll have to feed these fish extra food, don't think let them clean the aquarium is enough. Try cumcumber for their vegetable diet (don't try salad, it decays to quickly).
- Don't use a vacuum siphon on the bottom when your keeping corydoras or something like that. You'll take away their food and they'll have to search for food on the surface, their not made to do that.
- Keep real plants for oxygen and only use an O2 diffussor on the outlet of your filter and an aerator at night. To many aeration causes the carbondioxide to be absorbed by the air. This causes disbalance in cation-anion ratios and consequently increases the pH.

Mamohau (author)2010-12-19

don't tell him off for the dirty tank! He did say it was just as an example for the instructable and that it should never get this dirty!
Salt - don't use if you have snails! I have trumpet and ramshorns living happily beside the fish but it means I can't treat with salt if there's a health problem so I just use a 1%/100ml tea trea solution (as in Melafix). doestn't seem to bother the snails but one fish who seems to have gained a small wound is healing well.

lazemaple (author)2010-11-19

A very well thought out instructable all together! Good advice regarding safety which many instructables lack. The salt issue is one that experts still debate.
Removing the fish isn't always necessary then again with small tanks with only a fish or two its not a problem! Fish are intelligent and get to know their caregiver and the routine well enough!
I knew someone who had a very large goldfish in a 5 gallon tank she cleaned daily while removing him to a bucket. No bubbler or filtration either! She had him 12 years that I knew of and refused offers of bigger tanks... what else can you do? I lost touch with her so I don't know how old this fish lived or if he still lives! :-)
Its not something I would ever recommend! A goldie 3" or a bit bigger needs at LEAST a 30 gallon tank. Rule of thumb is 10 gal per inch of fish I think

lazemaple (author)2010-11-19

you can save loads of $$$ buy using Kosher or Pickling salt at a 1$ or less a pound! It has to be NON IODIZED salt with no caking agents and you can purchase right in the local grocery store.
I've used pickling salt for more than 5 years now in my brackish tanks and for curing any ailments

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