Water smells bad. Where is it from?


Hi.  I find that my tank water once in a while smells very bad.  I am not sure how to describe the smell but it strong enough to notice in the apartment.  And it comes and goes.  I would like to understand the origine and maybe find solution for it.
Here is the tank description.

45US Gallon
water surface 18"x36"
all interior surface made of natural stones
6 kois lengths ranging from 4 to 6 inches each
no plants
under direct sun light daily for 1 hour
2 airstones
1 external astro filter 2208
1 internal powerhead style filter


How many gallons per hour do your two filters pump (the total)? How often to you perform water changes and how much water do you change with each water change?

There can be many causes for smelly water. But I think the most likely one is stagnancy of water. If there is not enough of water circulation in the tank, the water may become stagnant and therefore smelly. I suppose an accumulation of fish wastes may cause smelly water as well.
  • Thread Starter


The main external filter does the 450 L/hr.  The specification label  on the filter says Qmax=450L/hr & Hmax=1.7m.
The internal filter is 600L/hr (based on the spec label).  I recently added this internal filter this week.
I change 25% water of water weekly.
The main external filter is cleaned & replaced with new NH3 rocks & carbon monthly.


OK, let me see if I got it correctly. Your tank is 45 US gallons in size. This equals to about 170 Liters, correct? Your 2 filters give you a total of 1050 Liter per hour of filtration (which is about 277 US gallons per hour).

Now, you usually want a filter (or filters) that pump at least 10 times the volume of your tank per 1 hour. So if your tank is 45 gallons (170 Liters), you should aI'm for filtration of around 450 gallons per hour (1700 Liters).

Maybe the smelly water is the result of not enough filtration? 1050 Liters/277 gallons seems like too little filtration for a 170 Liter/45 gallon tank - it should be closer to 1700Liters/450gallons.

Also, what do you mean by NH3 (ammonia) rocks?


I agree with Isabella. I think you need more filtration. I also believe your tank is way overstocked. What are you ammonia, nitrite, and nitrate levels. When I have had ammonia problems in my big tank in the past, I could smell it. I'd also bump up my water changes to 50% weekly if not twice a week.


HI indrpd, Your tank is stocked with 6 koi? Are you planning on using them in a pond? I ask this because usually koI are thought to be one of THE messiest fish you can keep, much worse than gold fish, and grow so large they are not suited for aquariums. Like gold fish they can tolerate much colder temps. After several years they can reach 3'+ each. They are already creating large amounts of waste, and your filters may not be able to keep up, even with the recommended 10 X the volume of your tank / hr.

They are in the carp family, and so are able to put up with worse conditions than tropical fish, but for healthy fish they need to have just as clear and clean conditions if possible, not to mention it will be more pleasant for you.

As I have told the fishlore folks before I would love to have a pond, and have always wanted koi, but chose tropicals for my indoor tanks, just because of the "waste problems".

Fish in the Frozen North. -6F this morning.

Most photos, videos and links are disabled if you are not logged in.

Log in or register to view

Top Bottom