Tips for Cardinal Tetras

[jesusjones]

I have been keeping cardinal tetras for maybe 4 years now and think I have finally figured at least one thing that may help out some others. My Cardinals have always been very skittish and sorta seemed stressed. They would eat, but sometimes lose there appetite for a day or two and they would always be hiding and schooling in the back, riding the glass and all sorts of stressed looking activities.

Adding wood decor and plants that extend from the substrate all the way to the surface seems to create an environment where they feel safer. They like to hide and relax in the shadows but also like to be able to see out into the open. I had black substrate (Flourite) originally that I changed out to sand for them also. The sand is less sharp and more natural to them. They will poke about in the sand but always seemed to be weary of the black sharp substrate.

But even with all this my fish always seemed to be on very high alert, like they could sense something. So, eventually, I'm poking around my tank with a voltmeter and I measure some voltage in the water of the tank (this is referred to as stray voltage by some and not well understood by most). The canister filter inside my tank had some leakage, in fact all my tanks with an impeller pump measure some voltage! But most fish don't seem to care or notice. That is where I think Cardinal tetras differ though, Cardinals come from soft, non-conductive, water and therefor probably have a higher ability to sense electrical signals in the water than other species (fish have electrical sensory organs). They need to be more sensitive to it because the signals are normally so weak in the soft water they naturally come from. Now, put them into a tank with much harder, conductive, water and the electrical signals from anything will be overpowering for their senses (I figure). So I took out the impeller pump and added sponge filters running on air. They calmed right down, still skittish fish for sure, but they always have an appetite, never glass surf and just seem happier.

So I recommend, for keeping cardinals, to not have any impeller pumps that may cause electrical noise/signals in the water. I'll see if I can get a photo up later to share.
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[GaryE]

Interesting. Just speculating, but I know some of their predators locate prey by sending out weak electrical pulses.

I find shading from above, heavy planting and wood up towards the surface overhanging makes them be very out and about. Bareness is death when you're that size

I'm into my 3rd major group of cardinals. i bought 50 and got 7 years out of them, then got 100, and had to move them out after 5 years, when I moved. I just restarted a bunch of wild caughts, and they are very outgoing, within limits. I use a canister and 2 HOBs on their 75 gallon/280 liter tank.

 

[jesusjones]

It was a lot like they thought a predator was lurking around the corner all the time. I have had around 25, but struggled to keep them thriving. They would do OK, but seemed stressed as mentioned. One by one, over time, they would get ill, white tumor growths at the tail base, bloat or getting very skinny. I thought maybe my tank was infected with something. With the fish now showing less signs of stress these random illness issues have also stopped.

I'll add that having more than enough filtration for them is probably more important than worrying about impeller pumps and "stray voltage". It is possible that the canister filter I used might of been undersized for the bioload and caused my issues. It was 70GPh with a fist sized block of foam inside, tank is ~25 G with only 15 cardinals max. Now, using 2 fist sized bubble filters, things seem better. But unplugging that canister did always seemed to have a calming effect.....

I chased this "issue" for a while, hope some of this helps someone figure out their skittish fish ​

 

[davros]

I wonder if it was enough current to trip a GFI

 

[jesusjones]

I wonder if it was enough current to trip a GFI

Good question and reminds me of a relevant story. I just now went to test it out in a bucket, plugged the filter into a gfi outlet and ran a ground from the same outlet into the bucket. It did not trip, it ran in the bucket for a few minutes while I checked some things.

With the bucket of of water grounded you can not measure any voltage between the water and ground (normal). When you disconnect the bucket ground there is a reading of 30 VAC in the water (odd, but seems normal from the pumps I've tested). The voltage increases slightly when you measure closer to the pump/power cord (pump is the source). Does it actually leak enough to be a hazard or matter?...the GFI outlet didn't seem to think so.

The story and another reason I suspected the pump. One time, the tank was on a basement concrete floor and I was barefoot (with water everywhere probably), sticking my hand into the tank I was clearly feeling a some mild tingling of an electrical shock, like acidic water on rough hands. I was more careful to wear shoes after that but didn't think much of it at that moment.

 

[jesusjones]

More Tips! Since last posting, I have spotted my my fish doing a lot of breeding behavior and even saw a cloud of eggs! I'll try and share what I've noticed about them breeding.

Seems to me, breeding behavior is triggered by large rain systems or seasons. The fish sense the pressure changes and possibly the difference in natural lighting from windows. The real kicker to get them going is doing a partial water change with some cooler water. The dip in temperature seems to be the final cue and they stay pretty active as long as the weather system is in the area. Most happens in the evening, the final 2 hours before lights out they just kinda go nuts all over the tank.

The fish (as always) should be well fed, large feeding of live food in particular seems to wake them up. Beyond having hardwood in the tank no effort is made to alter the waters pH. The water supplied has a pH >7 and around 150ppm tds and total alkalinity of 66ppm.

It is entertaining to watch, but whether or not the eggs are viable or could be recovered is another question I can't yet answer. But if you have a thunderstorm approaching go see what your cardinal are up to!​

 

[jesusjones]

Some new ideas and observations,
(My) Cardinal tetras don't tolerate high (normal?) light levels. Bright lighting has ultimately lead to increased stress and disease issues with this fish. They are noticeably on edge/stressed during their light cycle and there is only around 5w of LED lighting on a 25 G tank.

Why, maybe?... Cardinal tetras (probably others too) evolved to live in low light conditions, specifically their eyes. There is only so much a fishes eye can compensate for lighting conditions and for cardinals the limit on brightness is (seemingly) pretty low. Normally, fish will migrate (as much as possible) to whatever light conditions suit their eyes capabilities, they want to be able to see for their own sake. With cardinals, they always seek out dimmer areas of the tank, streams or flooded forests to spend their lives in, their eyes need/want lower light levels to work optimally.

It could also be a prey/predator instinct, where the cardinals know they are at higher risk in brightly lit areas (birds and such).

How much light? Imagine what the sun would be like shining through a large green leaf, that seems to be better for them. It would be something like 1/2 watt of incandescent for every gallon. If your cardinals are the type to hide a lot, try reducing the light or even turning it off to see how their behavior changes.

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[Byron]

You have made some very useful and reasoned observations. The current from filter motors I had not thought of, but I certainly think it is likely relevant. Water changes with cooler (some are now suggesting warmer) water replicates the oncoming rainstorm, and doing the water change on an overcast day can help as the fish do sense atmospheric pressure. And the light has been scientifically documented for this species. Observations in the habitat showed that the species avoided direct sunlight; the boundary of their range exactly coincided with the dividing line between direct sunlight and shade provided by overhanging vegetation. The authors of the five-volume Aquarium Atlas, Baensch and Riehl, used the term "light phobia." Nice work.