Ammonia Reading In 9 Month Old Tank- Help!

[JALouis]

HI,

My 55 gallon tank has been fishless cycled (thanks to the help of people here) and has had fish in the tank for at least 4 months. All of a sudden I started getting an ammonia reading of .25. This time I'm struggling with getting the level down. I've been doing frequently water changes (all along weekly about 25% and just recently every 3 days about 25% to get try to get the ammonia levels down). The nitrite are 0 and have not moved. The Nitrate level hasn't gone above 20ppm since the tank cycled. The water is pretty clean and there is not much coming up when I siphon (vacuum) the gravel. I do use a tap water conditioner before adding new water into the tank. The temperature stays stable at around 75 degrees.

I noticed last month a similar thing happened that the ammonia rose but then I changed the filter media (it was time anyway) and the ammonia dropped back to zero. This weekend the filter is due for a media change. Could this be a reason why the ammonia has started to rise? Could the carbon (there are 2 bags in the canister filter) be pushing the ammonia back out? I change the carbon when I change the filter sponge which is once a month usually at the end of the month.

I have to admit the tank is slightly overstocked (based on the full size of the fish though they aren't there full size). In the tank are 5 bosemani rainbow fish (who surprisingly seem perfectly fine and happy), 6 tiger barbs (one seems to be affected by the ammonia level and is struggling), 2 fan shrimp (who even with the ammonia level have been molting) and a black ghost (who seems perfectly happy as well. No slits in the fins).

Does anyone have any ideas as to why the ammonia increased and why I can't get it back down to 0?

Any suggestions would be helpful.

Thank you!

 

[ellena]

You shouldn't change the filter sponges. That's where all the bacteria live that you spent so long cultivating in the fishless cycle. Just rinse them in tank water and they will last for years. You're causing a mini cycle evey time you change them, which would give ammonia readings as the colony gets established again. You don't really need carbon in there either, only if you're removing meds

 

[JALouis]

You shouldn't change the filter sponges. That's where all the bacteria live that you spent so long cultivating in the fishless cycle. Just rinse them in tank water and they will last for years. You're causing a mini cycle evey time you change them, which would give ammonia readings as the colony gets established again. You don't really need carbon in there either, only if you're removing meds

Thank you. That is helpful. I can't remember if I change the sponge each time or the floss. I can only tell when looking at it. If I do change the sponge I will not do it this time.

Thank you.