I have 2 tiger oscar cichlids (Calvin and Hobbes). They are only 7 inches right now. Every morning I turn on their aquarium light and walk away. They tend to be groggy right away I find, so I like to give them a few minutes to wake up. Well, THIS MORNING (earlier than usual), I heard a commotion in the tank. I went over and Calvin was swimming frantically, running into the gravel, walls, rocks and plants and periodically jumping from the surface. He did so for about 1/2 minute. Then he stopped and I looked for Hobbes. He was laying sideways on the top of the water right under where the filter spits out water. I was worried he was dead so I touched him and he copied Calvin and swam frantically.

Additionally, a few days ago they broke a thermometer in their tank but I'm 99.9% certain there is no mercury in it.

Now, about 13 hours later, they seem completely fine, but perhaps a little pale. What's wrong... what can I do? I know the tank needs a cleaning right now and I intended to tomorrow (and still do), but I wouldn't say it is dirty enough to cause this sort of problem. There has to be something else.

99% of the time, water conditions are responsible for fish death or illness. First thing you need to do to check the water parameters. That is ammonia, nitrite, nitrate and pH. Ammonia and nitrite should be Zero and no higher.

I've got to be honest with you, I have absolutely no idea why your fish were behaving like this. Fish are probably the most difficult creatures to diagnose when something is wrong. Want we know your water readings, we might be a will to rule a few things out.However, we may never know why you're fish behave like this. I've seen my fish behaving strangely and haven't been able to fathom out why.

It could well be that your fish were still asleep when you turn the lights on.

welcome to the site!

by just looking at the water, no one could ever tell if is dirty or not. clear water doesn't mean it is okey. ammonia? nitrite? nitrate? the three common elements in water that can causes fish problem. pH and temperature may also contribute. please do check and post.

any sudden changes in fish attitude such as darting; gasping; not moving; and not eating are already sign of potential problem. giving us the water parameters will help us help you.

I did not just look. I went to Petco and had all the levels tested. Everything was fine, except as seems unavoidable with oscars, the nitrite (or am I thinking nitrate, the one when its dirty... I can't remember the difference) levels. Again, I know I am due for a cleaning and intend to do so tomorrow. But I don't want to miss out on some other potentially important treatments before it is too late. Thanks

They do move things in the tank around a lot, and seem to use the gravel as a launch pad for occasional darting, but this was not the same... and for significantly longer. I am not concerned about occasional darting. I think that is just their personality. (Also, no, I don't believe the way they launch off the gravel is itching because of parasites.)

moving substrates in not taking lunch out of
sand, it is their natural behavior. occasional
darting that banged the glass wall... you should
worry on that. the fish is trying to say "hey,
i am not comfortable with this place, please check"
swimming without injury, that would always be fine.

Not lunch... they use it to "launch",(in land terms) jump, I guess. I am hoping the cleaning will make them feel better, and thus they will not sun into things.

sorry, i mis-read along the line.

of course. water change and cleaning will make your
fish feel comfortable. pristine water is the first
health defense of all fishes

My prof (fish biol) recommended beginning a brand new tank (100% new water) for them... of course leaving it sit to get started. I have 2 tank (although one is too small), so this should not be too hard.

They did it again this morning, this time before I turned the light on. And both at the same time. Hobbes floated after hitting the wall, kind of making me think he knocked himself out. Both times afterward they went and sat in the same corner by the filter and acted like they couldn't swim. and then a few minutes later, they were fine. Any hints on making a new tank I might not have picked up?

I would carry out of 50% water change and see if it makes any difference. Also, I would try and get an understanding of the differences between the toxins that can buildup in the water. Ammonia and nitrite are highly toxic and will kill fish, your reading should always be Zero. If you have a healthy biological filter then you shouldn't ever get ammonia or nitrite building up. If you have too many fish or maybe overfeed, you may get what we call an ammonia or nitrite spike. Your biological filter will remove ammonia and nitrite. On the other hand, nitrates is a byproduct of ammonia and nitrite and this element is kept under control by carrying out water changes. Whereas nitrate is not as toxic as ammonia or nitrite, it should be kept below 40 ppm possible. If it gets too high, it can stress your fish. Nitrate normally gets very high if you don't clean your tank enough.

If your fish are hanging around the filter inlet, that sometimes points to poor water quality. I would strongly urge you to get yourself some liquid tests so that you can carry out your own water quality tests. Please don't worry, they are very easy to do. The only one that can give you problems (as in false readings) is the nitrate test, this normally only happens if you don't read the instructions properly.

OK- I did a 50% water change this morning, and of course siphoned the gravel, and as recommended I bought a test kit. PETCO lied to me. I ran all the tests:

Ammonia was less than .25 but not 0
Nitrate was (estimating) 100, higher than 80, but much less than 160
Nitrite was .25
and PH was low for Oscars at only 7.4

This was after the cleaning. So I can't disturb the water again for at least a few days right? The fish are currently in my 14 gal (way too small, but it will have to do for now) which I filled with 7 gal the water from the other tank and 7 gal new water. What now? How can I fix this?

first off keep doing water changes until both your ammonia and nitrites read and stay at zero all the time. this is very important as both of these toxins are extremly hazzardous to your oscars. as for the nitrates when they reach 40 ppm it is time to do a water change. but since your primary concern is the ammonia and nitrites getting these to 0 will lower your nitrates.

as for the ph oscar can tolerate a wide range of ph values. anything between 6 and 8 is acceptable. the key to ph is to keep it stable. if it calms you at all my oscars live in a tank with a ph of around 6.4 and they are healthy and happy. i would not recommend playing around with your ph unless it is absolutly necessary.