My Oscar began acting very strangely about a month ago after my friends kid overfed him - he was thrashing around and scraping himself up pretty bad against the ornaments, and had long stringy things under his belly. I assessed that he had an internal parasite and treated using Jungle Labs tablets. The good news is the thrashing has stopped and he seems calm. The bad news is that he hasn't eaten in 3 weeks (that I've seen) and won't even come up to feed. He used to jump halfway out of the tank and take pellets from my hand, now he wants no part of it. His roommate, a tiger oscar, is fine and eating like a champ. Is it possible he has sustained damage from the parasite and can't eat? I know he can't go on for much longer not eating!

Also: not sure if this is coincidence but the two of them have been lip-locking here and there and a lot of tail-shimmys - I'm interpreting this as mating ritual but could be fighting I guess - although they swim around together all the time and seem to like each other.

welcome to our little community

I can tell you now, Oscars stopping eating is so bloody common, you wouldn't believe it. I have got an Oscar at the moment is sustained an eye injury a few weeks ago. I have a feeling that he is now blind in one eye. Anyway, he wouldn't eat, as soon as I put food and he would go and hide. I started treating my tank with vitamins about five days ago and in the last couple of days he is suddenly showing an interest in food, although not going too mad. Now, whether this is down to the vitamins I really don't know, but I'm very hopeful that he will learn to live with one eye. Even better, these vitamins might even help with his eye, but I'm not a hold my breath.

Okay, have you tested your water? Please do that, Ammonia, nitrites, nitrates and pH. I know that this is something we ask nearly every time, and we have been accused of behaving like a broken record, but it is so very important that we know what your water quality is.

Try feeding some frozen krill of shrimp, or some frozen fish from your fish store, something like Lance Fish, you never know, your oscar may suddenly start eating these.

I wish I could give you a conclusive answer to why your fish is doing this, unfortunately it is one of those things that Oscars seem to have a trait of doing.

Thanks for the fast response! My tank is 55 gal, 78 degrees, ammonia is 1.0 ppm and nitrates are about 7. Not sure why ammonia has been high last few days, been doing 35% water changes and treating with AmQuel but still not 0?

how long has this tank being set up? An ammonia of 1.0 is not very good unfortunately, your fish probably will not like that. Please don't put too much food in and feed sparingly until the ammonia drops. What is the pH and nitrite?

about 2 yrs - yes was surprised by the ammonia spike my inability to reduce it with water changes and amquel?? what could be the reason for that level not subsiding? this is 3rd day its been above zero. measuring other levels now...

What is your pH? You might want to check your filtration and make sure there are no blockages anywhere, if the water is not running through it properly this could be the reason for the ammonia.I would suggest that you actually stop feeding for a couple of days. This will help reduce the amount of waste that your fish produces thus cutting down on the ammonia going into the water

Have you done anything differently in the last few days, maybe cleaned your media out in tap water or something like that?

oh no - I did clean my filtration system in the sink and replace the filters - did I remove nitrites that were keeping ammonia in check? (checking PH now)

High Range PH is 7.4, Nitrites .50 ammonia 1.5 - climbing again!

What type of filters have you got? Which media did you replace?

You need to get a basic understanding of how your filter works. I'll give you a quick rundown. A fish produces ammonia through respiration and their waste. Ammonia is a very dangerous toxin that will kill fish. Inside your filter you have bacteria that live on the media. Some of the bacteria will consume the ammonia and basically they will then turn this into nitrite. Then other types of bacteria will consume the nitrite and turn this into nitrates. You then to water change to reduce and keep nitrate low.

If you kill your bacteria then you will have no means of controlling the ammonia. One of the easiest ways to kill all your bacteria is to wash it out in tap water that contains chlorine, after all chlorine is there to kill bacteria in the first place.

So when you set your filters up you've got to be very careful. They will meet cleaning and some of the media will meet changing occasionally, but normally only the media that actually remove solid waste and gets dirty very quickly. The bar logical filtration is a very important part of your filter and you really shouldn't change this at all, just clean this type of media in existing tank water every now and then.

I don't know whether you have killed off all your bacteria or whether you still have some in your filter. If you've killed it all when you are going to get very high readings of ammonia before too long.

are you using aquarium pharmaceuticals liquid test kits? Have you got a low range pH kit?

It sounds like your tank is going through the cycle again.

thanks for taking the time to explain in detail, I had thought the bacteria lived more in the substrate (gravel) than in the filter cartridges. So when you say media, I assume you are referring to the 2 filters cartridges I have in my filter? They are mesh with carbon inside. I will have to look up "bar logical" so I you don't have to explain that to me again as well. Thanks again for helping a newbie out!

I assume that you have got some HOB filters. I'm not really familiar with this type of filters because they are not very popular over here in the UK. What I will say is I would strongly advise you to remove the carbon. Sorry, yes, the media will be your cartridges. Somebody else will probably be more familiar with these type of filters than I am