I keep a school of 15+ in an 82 degree discus tank with in hard water.
I do weekly 50% w/c and they seem to be the first fish out of the plants,apparently reacting to the nutrients stirred,triggering a feeding activity
Cardinal tetras are extremely hardy once they have been acclimated. However, most in the hobby are wild-caught and so have not only been exposed to pathogens, but with capture and handling stress are often in very poor shape by the time they get into a hobbyist's possession. I highly recommend both drip-acclimation plus a lengthy quarantine in 1/2tsp non-iodized salt per gallon, 2 weeks minimum. These fish are extremely susceptible to fungus and ich- do not buy them if any other fish in the LFS is displaying symptoms. They prefer higher temperatures than neon tetras, and are great dither fish with discus.
They are from waters with kH -3 gH -5 so in hard water as mine females become fat (eggs cant go off) But this fish MUST be in good planted tanks -green plants-red neons together makes good colour combination. School-means -from 20-40 fishes.
Not much to say than "AWESOME FISH".. Color are much greater than the NEONs.. Just a little suggestion : If you have medium or large aquarium try to get minimum 20 of this fish to give them a better psychological field that will effect their confidence and their social behavior and finally will effect their ability for staying alive and body immune :)
These are absolutely my favorite fish. They're very hardy once acclimated, so make sure to acclimate them well. They'll eat all types of food, and their spectacular colors make them an excellent fish for a planted tank. They're more outgoing in larger groups of at least 7 or so, any less than that and they may be a bit shy.
Lovely Fish but so delicate! I have an heavily planted tank, ph, hardness and temperature in the suggested range for these guys. I bought 7 for beeing sure they would have been schooling properly. I gradually mixed the shop water with the aquarium one, giving the proper time for temperature and parameters to set. They did great for 2 days. Then I found 3 of them dead in some bushy plants. The next day other 2 were dead and the third day the remaining 2 were sadly dead. Great looking fish but really delicate and expensive, considering that is ranges between 5 to 8 dollars and you need at least 6 of them to school...
The Cardinal Tetra is one of my favorite fish. I have a school of two dozen in my 30 gallon planted tank. The fish I have now were tank bred and are very hardy. Since they were shipped to me by mail I did no acclimation (just floated the bags to equalize the temps) when I added them to my tank and I didn't lose a single fish. I feel like a long slow drip acclamation does more harm than good by stressing the fish out. Be careful when getting these fish that you can trust the source. Once I had a healthy school of 12 and decided that I would add five more too. I got the other (overpriced) tetras from a LFS and within a week they had killed off almost all of the original school. So if the fish are healthy when you get them they will be hardy... If they are unhealthy they will more than likely die.
These have got to be one of my favorite fish! They're very colourful, peaceful, and very hardy once acclimated into your tank. They make for a stunning display in a planted tank with rummynose tetras! Keeping these little guys for the first two weeks can be a little tricky. If they survive the first two weeks, they're set to live a long life. I have 9 of these guys (planning on at least doubling the school size) in my 55 gallon planted tank with a school of rummynose tetras and a few other small fish... They make the tank :)