An aquarium question

Question
Hello Nathan,

I am interested in keeping some Cardinal Tetras. Right now, I have a 20 gallon aquarium with 4 Zebra Danios (my cycling fish). My cycle is complete, and I'd like to add some Cardinal Tetras.

Will the fish be compatible? (I;m only going to have 2 species)
How many Cardinals can I add?

Thanks, and I hope to hear from you soon.

Answer
Hi Martha,

Good Job with your aquarium! You'd be surprised how many people skip the cycling process, which results in dead fish!

Cardinal Tetras are compatible with Zebra Danios. It is only the Bigger Tetras that get stressed by fast moving fish. You can add up to 6-8 Cardinal Tetras, but add a maximum of 3 at a time to keep the delicate parameters of your tank in check. Cardinal Tetras are known to be picky about water conditions, so careful acclimatization is a must. If you cannot drip-acclimatize them, I highly recommend staggering the water change intervals during introduction to about 25% every 5 minutes.

OK, here's the understandable version :)
-When buying them, check for bright colors, shoaling behavior, and swimming
-Don't buy fish you think are sick! If you see a sick fish, don't buy from that tank!
-After you buy the fish, float the bag in the aquarium (with lights turned off) to equalize temp.
-Do the above for 15 minutes. This is important.
-After that, untie the bag and take out approximately a quarter of the water in the bag.
-Discard that water, and re-fill the bag with a quarter aquarium water.
-5-10 minutes later, take out another quarter of the bag water, filling it with a quarter tank water, discarding the bag water.
-Another 5-10 minutes later, do the same thing.
-Repeat this once more, after 5-10 minutes.

By now, about 75% of the water in the bag is tank water. The Tetras will have become used to your water, and now, you can carefully net them out. Don't pour the bag water into the tank, because the risk of transmitting disease from the pet store aquarium to yours is high.

Good Luck, and Happy Fishkeeping!