Hi, I have two young common goldfish  2" from nose to tail end and am having serious problems with the water. At the moment they are in approximately 14" by 7" lidded bowl with vented roof. The water is literally fouling so much after 2 days, that I can smell it a room away. I change a little of the water as recommended, it still smells.
I usually filter the water and use crystals for cleaning it, as it tastes/smells of chlorine or sulphur (I drink bottled most of the time) The gravel goes black, as do the ferns. It won't even last a week (with recommended taking out and topping up) and that is when I have taken all the gravel and ferns out
It is starting to become a real concern, especially as the fish are being disturbed so often. I have to keep taking them out to clean the bowl. I don't know of anybody who has had this problem when keeping their fish in an ordinary round bowl. 
I do not have space or the ability to deal with a large aquarium, especially if I am going to have to start buying  bottled water to fill it..
Any advice?
Thanks
Cristina

Try reading under discussion /General/Do goldfish mind algae in their tank?

I always belief good water quality is about good water management. Is mainly about bringing the waste level down. Most filter take care of the solid waste and the bacteria in it normally breaks it down to nutriens. Just because there is no debri doesn't mean the water is good. Some form of element should be managing the nutrien built up before it reachs to a poisionous level. It can be human intervention (changing of water) or by nature (choosing the correct plant). the best is combination of both. Hope it helps you.