Should I remove sick fish?

[Xeider]

Currently running a 20 gallon tall with a penguin 170, whisper heater, fine gravel substrate, mildly planted tank.

One of my zebra danio (I currently have 5 zebra, and 1 panda cory) has been acting odd all day. I came in this morning to find it laying on the bottom, and it looked to be dead. It wasn't but has ben barely swimming all day, and tends to lay down on the gravel until another fish bothers it. It had not been moving for over an hour, and I thought it was dead (some fish were moving around it, and it didn't respond) so I went to remove it, and when I got down there with a net it started moving again.

I am wondering if I should remove this fish for the health of the other in the tank because I am not sure what is wrong with this one. When I got in this morning, I found one of my panda cory dead on the filter intake, and a third panda I had is missing. Everyone else in the tank seems fine (though I see a very small snail that looked to have stowed away on some recently added plant (2 java ferns, crypt, water sprite)).

Should I remove the ailing zebra, or give him a few days to see if it recovers?

thanks!

[wetmanNY]

It's always wise to remove dying fish.

Something is toxic in your tank. Have you done a test for nitrites? (Not to be confused with nitrates, which are fairly harmless.)

[Xeider]

All the test have come back ok so far (Nitrate NO3 <20 ppm, Nitrite NO2 <.25 ppm, Ammonia 0, pH 6.8)

If I don't see a noticable improvement today, I will be removing it. I am more worried that it will die from lack of food, as it hasn't made a move to eat at feeding time. It also seems to do a caotic swim were it swims around eratically like crazy often bumping into the gravel, rocks and the glass. Mostly it likes to find a quite spot and lay down and stay motionless.

[Faramir]

That's a dying fish if ever I saw one.

It won't die from lack of food - fish can last weeks without eating - but it will die from whatever's causing its symptoms. Could be acute organ failure, a stroke, something like that. You'll never know. But it will not last long.