Sudden change in fish behaviour

rebe

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Hello, I'm hoping somebody might have some insights into what is happening with my fish. I have a 75g with 40 tiger barbs and they have always been the most outgoing, friendly and active fish. Today I noticed they are behaving as if they are frightened and just hiding behind the plants at substrate level. When occasionally I see a few swim out from the plants, they dart around near the substrate before hiding again. Their behaviour just seems frightened to me. I tried a sprinkle of food to see if they would eat (these barbs are greedy pigs always) and they were not as excited and quick to feed, but still came out to eat.
Nothing has changed in the room, and the tank temp is the same as always. No ammonia, nitrite or excess nitrate. The light and filter seems to be functioning normally.

The most recent change to the tank, was I started adding adding co2. This was over two weeks ago, and the barbs didn't seem to care at all. Is this some sort of weird delayed reaction?
I use a ph controller for the co2, so it's not a malfunction in the system unless the controller is now taking a false reading and injecting too much co2. That must be highly unlikely though? All of the co2 equipment was brand new, and I calibrated the controller properly.
 
I've seen such weird behaviour and done massive water changes, which made it vanish. That's my default 'something's off' response.

I have also seen it be a warning sign of Ich, with recently bought fish. That's not your issue here, with established ones. Hmmm.
 
@GaryE Thanks for your reply, I think I'll do 70-80% water change in the morning. I hope that will help them. I'd rather do a water change and it do nothing, than to worry about not having done one.

The tank has been running a long time, and the fish aren't new either. So I doubt it's disease but I will watch them as carefully as I can for any other symptoms
 
I've not experienced it but have heard about stray current from cracked heaters/ dodgy lights?
Also it would be worth verifying a few pH readings over a 24 hour period?
 
I did have one tank that got weird where when I put my hand in, I got zapped - there was a tiny crack in the heater. Thanks @Naughts for raising that. It's worth considering. I have had electrical leakage from a couple of heaters, and older powerheads. I now keep fish from the cooler side of the tropical spectrum and don't use heaters.

Unplug the heater before you do work and give it a very thorough examination.
 
CO2-Related Issues (Most Likely)‌.Even if your pH controller is calibrated, CO2 injection can indirectly stress fish in subtle ways.
High CO2 levels reduce oxygen availability, especially at night when plants aren’t photosynthesizing. Check for rapid gill movement or fish gasping at the surface.
 
@Naughts @GaryE Thank you, an electrical fault did come to mind. I will have a look at my equipment soon as I can.
I noticed that the fish seemed better this morning before the tank lights came on. They seemed frightened again after the tank lights came on. So I've turned off the tank lights to see if they calm down. I hope the lights aren't the issue, as this is the tank with plants I'm trying to grow. I did increase the duration of the tank lights by an hour recently, I wonder if that's causing them to panic 🤔
 
Do your light have gradual transition when lightning up / shutting down ?
 
Check the water quality for ammonia, nitrite, nitrate and pH.
Check the water chemistry for general hardness and carbonate hardness.

When fish suddenly hide and stress it's just about always from something in the water.

As Gary suggested, do a massive water change and gravel clean the substrate. Make sure the filter is running and turn the CO2 off until you can get the oxygen and CO2 levels in the water tested.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
 

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