Question: Acid smell in the tank

[Sasha]

About 4 months ago I bought Eheim Classic filter, after using it for a month I stopped it, and did`t use for 3 months. Right after stopping the filter I washed all the pads and substrate, so when I started it again I didn`t change any of them and run it as it was. Also I put Onyx Sand in the tank instead of river rocks I used to have before. The water in the tank has very strong acid smell now (before it never happened). Today I washed the filter and the sand, but smell is still there. What may be the reason? Is the problem in the filter or the sand? What should I do?

 

[Aimee]

What are the water parameters? Do you have any animals in the tank? How long had the tank been set up before buying the new filter?

 

[michael]

If the pads and substrate were not dried completely they probably went anaerobic. This means instead of cleaning the tank you are polluting it with your filter. If this is the case I would clean the filter and replace all of the pads and medium. I would also do a complete water change on the tank.