[snafuspyramid]

My tank is smelly.

Not two-Apple-snails-died-last-week-and-are-rotting-somewhere smelly (I've been there). But there's still that distinct sulphurous odour that indicates something's up.

All inhabitants are present and correct; there's no rotting plant growth (well, not more than usual); and I haven't used any medications, or changed any parameters.

The tank is a rather overstocked, very well-established 90 gallon. It's quite heavily planted - about 25% volume. No CO2, just homebrew Excel and ferts. It gets 25% WC weekly, and has slightly over-adequate filtration cleaned regularly (a 2217 and 2215).

Parameters are normal, 0-0-10.

Noticed one of my angels has a bit of a fin tear, which might indicate quality issues, or might indicate that he likes getting violent with himself in confined spaces. (Wow, that sounds strange). Apart from that, no losses, diseases or unusual behaviours.

What might be causing the stinkiness?

 

[VeeSe]

Your tank has likely gone anaerobic, which means that bad bacteria are growing within the substrate and producing deadly gas bubbles that can be released, killing your fish. This is caused by pockets of substrate that oxygen can't reach, for example if your substrate is very fine sand and tightly packed, anaerobic pockets can form.

edit: It may be a significant amount of work, but one way to deal with this is to put your fish in a bucket of tank water, pull the plants out and dump them in another bucket of water, drain your tank, and swap out the substrate, getting rid of the septic smell (wipe your tank down in between taking out the old substrate and putting in the new, maybe with vinegar or something). Then, replant and put your fish back in after filling up. If somebody has more experience with this and has a better idea that is less work, then listen to them. But I know that this stuff can kill fish and you need to get it taken care of. Not sure if just poking at the area (if you find it) and releasing the gas pockets will work, or if you caught it early enough for that.

 

[wkndracer]

With clean filters add an air stone while working and stir up that substrate anywhere you have access with a chop stick or planting tweezers, fork, what ever works for you. Done in several sections, done on different days you can break this up. (dirt tanking trick)
HTH

 

[bsmith]

An anaerobic substrate could be it but I doubt it. Does it smell really earthy, like something you would expect if you picked up a rock in a slower flowing stream and gave it a sniff? You may have some BGA in there (cyanobacteria). That stuff has a very distinct aroma for sure but I find it strange that you would be smelling it in the room without having taken any of it out. Unless you have a HOB filter?

 

[snafuspyramid]

The smell is only faint, and only apparent when I am over the tank, changing the water or fiddling about. The tank does have deep sand substrate, although it has a pretty healthy population of MTS I was hoping would keep it turning over enough to stop it going anaerobic. Will try the airstone/chopstick technique. Definitely smells like sulphur

 

[Steve001]

My tank is smelly.

Not two-Apple-snails-died-last-week-and-are-rotting-somewhere smelly (I've been there). But there's still that distinct sulphurous odour that indicates something's up.

This means your substrate has become anaerobic. Your tank's water should at most have a very slight organic odor which is only detectable if you have to nearly stick your nose close enough to get it wet.

All inhabitants are present and correct; there's no rotting plant growth (well, not more than usual); and I haven't used any medications, or changed any parameters.

This is a vague statement meaning it's difficult to evaluate. With good plant management practices you should have very little die off of plants.

The tank is a rather overstocked, very well-established 90 gallon. It's quite heavily planted - about 25% volume. No CO2, just homebrew Excel and ferts. It gets 25% WC weekly, and has slightly over-adequate filtration cleaned regularly (a 2217 and 2215).

Overstocking at tank is a bad thing to do. It does not occur naturally and it should not occur ever in a tank.

25% is not a heavily planted tank. What you've got a a fish tank with some plants. A heavily planted tank is an arbitrary term, however, you can consider a tank that is 75% or more filled with rooted plants a heavily planted tank.

The one good thing are the weekly water changes

Noticed one of my angels has a bit of a fin tear, which might indicate quality issues, or might indicate that he likes getting violent with himself in confined spaces. (Wow, that sounds strange). Apart from that, no losses, diseases or unusual behaviours.

Reduce the population of fish.

What might be causing the stinkiness?

Overall poor tank management.
Suggestions:
1.Reduce the fish population or add if practical a second tank connected to your system to increase the water carrying capacity.
2. Add a lot more fast growing plants. See Plant Profiles at top of this page for easy to keep plants.

You should be able to remedy this situation fairly easily.
Good luck.