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What exactly causes the water to smell horrible?


5 Jun 2010
Canterbury, UK
My tank water smell's truly hideous, I have changed the water 90% and with in a day, it smell's bad again, I think it might be the soil substrate, could that be it? How can I stop this happening?
what does it smell like?

bga or cyanobacteria, smell very musty, not a great smell..

rotten eggs smell comes from hydrogen sulphide. this is caused by too much organics in your substrate, which bacteria are breaking down in an anaerobic environment releasing h2s2 as a waste product.

if your substrate has already gone anaerobic, you might need to look at redoing it. i am not sure adding malaysian trumpet snails will help, as they can prevent your substrate going that way, not so sure if they can undo it.

what substrate do you have?

soft driftwood is also a candidate for smelly water, basically anything that is rotting or being broken down by bacteria.
probably Cyano (BGA) or sometimes a dirty filter do the trick. not sure when you had a maintenance on that.

BGA can be removed by hand where it is possible. It happens when the flow is not enough. If that's the case drop in a Koralia to help you out. ADA Phyton Git also helps to attack and prevent BGA, but you need a continous movement all around the tank.
Hi Oliverar
Wearsbunnyslippers has probably got to the root of your problem.

You need to remove the soil and start again, using aquarium gravel/substrate or a sand thats not to small in grain size.3mm and larger would be ideal.

Add some fast growing rooting plants like vallisneria/hygrophlia polysperma/limnophila sessiliflora these will keep your soil in good condition.
Add some mature bacteria to the substrate from well established filter this will be beneficial for a new set-up.
Hi all
bga or cyanobacteria, smell very musty, not a great smell.
would be my suggestion as well. If you don't want an inert substrate, maybe go for smaller percentage soil in your substrate? I like the low nutrient approach and I use about 80 - 90% silica sand and 10 - 20% 1:1 clay and leafmould.

cheers Darrel