Warning: mysql_real_escape_string() expects parameter 2 to be resource, object given in /home/avery/homefishaquarium.org/public_html/wp-includes/wp-db.php on line 1173

Warning: mysql_real_escape_string() expects parameter 2 to be resource, object given in /home/avery/homefishaquarium.org/public_html/wp-includes/wp-db.php on line 1173
Cleaning a VERY Dirty Fish Tank | Home Fish Aquarium Guide

Home Fish Aquarium Guide

Fishkeeping Information and Resources for the Home Aquarium



Looking for even MORE information on freshwater aquariums?
Try the My Freshwater Aquarium Secrets ebook.

My Freshwater Aquarium Secrets



« Weathering an Extended Power Outage in a Fish Pet Tank

Choosing a Heater for your Tropical Fish Aquarium »

Cleaning a VERY Dirty Fish Tank


Warning: mysql_real_escape_string() expects parameter 2 to be resource, object given in /home/avery/homefishaquarium.org/public_html/wp-includes/wp-db.php on line 1173

Warning: mysql_real_escape_string() expects parameter 2 to be resource, object given in /home/avery/homefishaquarium.org/public_html/wp-includes/wp-db.php on line 1173

Warning: mysql_real_escape_string() expects parameter 2 to be resource, object given in /home/avery/homefishaquarium.org/public_html/wp-includes/wp-db.php on line 1173

Warning: mysql_real_escape_string() expects parameter 2 to be resource, object given in /home/avery/homefishaquarium.org/public_html/wp-includes/wp-db.php on line 1173

Warning: mysql_real_escape_string() expects parameter 2 to be resource, object given in /home/avery/homefishaquarium.org/public_html/wp-includes/wp-db.php on line 1173

Warning: mysql_real_escape_string() expects parameter 2 to be resource, object given in /home/avery/homefishaquarium.org/public_html/wp-includes/wp-db.php on line 1173

I have to report a follow up to the LAST confessional I had about our fish tank being very dirty. It seems every time I do a water change we will get an algae bloom within a couple days. Algae collects on the tank surfaces and then the water clears. I’ve pretty much left it when it does this until the next cleaning as our fish seems happy and content. The basic water parameters (ammonia/nitrite/nitrates) all seem at negligible levels. I’m still surprised that the nitrates are staying near zero and still assuming that the plant growth we have (and yes algae too likely) are keeping it that low. I can’t help but wonder if our well water is responsible for the algae blooms (phosphates?). So… how do you go about cleaning a VERY dirty tank?


I remember when I was little I heard someone talking about cleaning a fish tank and had visions of them getting a bowl of water to put their fish in and then empty out all the water from their tank and use cleaners and scrub everything down and then reconstruct it. In fact, when I asked my wife about her short-lived experience of having a fish when she was a girl that is pretty close to what they did. They didn’t have a fish long though.

In retrospect, and I hope if you’ve read the resources on this site you can see where that approach is a bad idea. Of course, there are beneficial bacteria that grow in a fish tank and you need them to survive or the water will become polluted with ammonia and nitrites (that you cannot necessarily see) and your fish will die.

But what about when the tank gets visibly filthy on the surfaces and gravel….. or what if the water parameters are getting too high. Our first instinct is to yank our fish out of there and move them to clean water, but again…. that’s a bad idea. Moving a fish from one tank to another can be stressful, the sudden change in water parameters such as the ammonia, nitrite, nitrates, ph and even temperature can be a shock to their system.

So… here’s what you do and this is what I did with my last cleaning. Before removing any water carefully use a brush to work your way around to all the surfaces (glass/lift tube/heater/other tubes/decorations) and dislodge as much of the accumulated stuff as possible. In our case I’m pretty sure it’s algae. This unfortunately will stir up a LOT of debris in the tank that your fish will be swimming in for a few moments. It is important though to do that first.

Next get your gravel vacuum ready and start using it to empty water and suck up the floating debris as well as any that might have settled on the gravel. I work through the gravel fairly indiscriminately of whether there are plants there or not. We have a clump of java moss that I most always prune a bit off with the pump and afterwards I’ll pick some back out of the water and place back in the tank, but…. plants are really fairly resilient and if they have survived for months under the same conditions a little pruning may even stimulate growth. I’ll also try to get some of the larger floating debris being careful not to break the surface and loose the suction of water.

Of course, be careful not to get your fish with the gravel vacuum!

A typical water change I’ll get about 1/5 of the water down to as much as 1/3 of the water out before stopping. Usually when I stop is determined by when I accidentally break the surface of the water with the vac while chasing a floating chunk of algae. However…. if it’s really dirty go for a 50% removal of water. I know you will be looking at the 50% that’s left and think that looks nasty with all the stuff floating in it, but if you have a good pump set up it won’t be that way for long. I then slowly refill with water that is about the same temperature as is in the tank.

I get it up to full and wait for the filter to do its job. Now, we have an undergravel filter and long periods without cleaning can actually lead to a buildup of dangerous gases within decomposing debris in the gravel. This is one reason many people dislike undergravel filters. So, when I clean I try to make it to every square inch of the gravel. Initially the tank still has debris floating in it, but after an hour or two the water clears to a whitish cloud and then by next morning it is crystal clear.

I’ve actually modified our under gravel filter a bit from the instructions that came with the tank. When we got the tank the instructions were to put activated carbon in the canister as a filter medium. Since then I have used polyester foam (like they use for stuffed animals or throw cushions.) That foam filler works as a floss medium and gives more surface area for the good bacteria to grow (since air is forced through the filter box and lift tube. But more than that it filters out even the tiniest particles that the activated carbon will miss. Activated carbon is a good media for creating lots of surface area, but particulate can get past it (and it always did). Since switching to half activated carbon and half “floss filter media” we have had crystal clear water (even when the glass covers up in algae.)

To put it more concisely it’s the best this tanks filter has ever performed to use a little bit of the foam/floss filler in the filter. The only thing I have to be careful about is putting too much in as that will bottle up the flow of air and water and will force air out through the gravel. So, don’t stuff it into your filter canister!

Now…. if you do a 50% water change because things are filthy and feel like you need to do more, then wait a day (or two) and then revisit with another deep cleaning. You really shouldn’t take more water out at a time than that even if things are dire! If things are dire then schedule those deep cleanings a bit closer together, but try to give time for things to stabilize between the cleanings.

Free PDF    Send article as PDF   
Tags: , , , , , , , , , , ,
January 3, 2010 - 1:21 PM
Leave a reply

CommentLuv badge