Cycling question with piranhas?

Question

I just bought 5- 2"piranhas and a 75 gallon tank. I went to a fish store that specializes in wild fish. The owner seems like he has a lot of knowledge and experience with fish. My question is he said for the first 6 weeks with the piranhas inside the tank I shouldn't do anything with the tank. So no water changes. That's how he told me the tank will cycle and grow bacteria. But I've been doing research and I've read that changing the water frequently is crucial to the cycling process. What should I do? He said since the fish are small and inside a big tank the ammonia levels won't be harmful.

Answer 1

The owner does have a point about the volume of water and the size of the fish, but this doesn't guarantee that your ammonia and nitrite won't get to harmful levels. A lot of how your cycling goes will also depend on your filtration and how much you feed.

You're really safest to use a test kit to monitor the ammonia and nitrite levels. Neither should be allowed to get above 0.5 ppm. At 1.0-1.25, these can become fatal to some species. If they start to approach these levels, do a 25% water change.

You have the advantage of starting with small fish, so as they (and their appetites and waste production) grow, the bacterial population will be able to grow as well.

Answer 2

He may be right,but only if you don't come anywhere near overfeeding the little guys. The way to cover your bet is to monitor the Ammonia levels in the tank. Most test kits have charts that will tell you how high to let the numbers go,and if the levels get above what ever the test kit suggests,then do some water changes,in this case information is power.
You should see the Ammonia numbers rise to a peak,in 3 or 4 weeks,and then a corresponding rise in the Nitrite numbers should begin and then peak in another 2 or 3 weeks, then, when the Nitrites also drop to nothing, your tank will have completed its basic cycle.

Answer 3

I always heard that when you first get fish, you do need to let them get used to their environments, no matter what kind of fish it is. I would probably wait about 3 weeks or so, then do the whole take 1/3 of the water out and replace it with new water about every week or maybe 2 weeks.

We had a piranha before and I think we changed the water every two weeks. We didn't have nearly as big of a tank as you did, but we took a big bucket and filled it with just plain tap water and let it sit from the time we just changed the water until the next time we changed it. With letting it sit, it gets the chlorine (I think it's the chlorine) or whatever the stuff that's harmful to fish out of the water without buying special chemicals. But there are some things you can put in the water at every change to be on the safe side.

We also had some Oscars, but we only changed their tanks about ever 3 or 4 weeks, and we did the whole thing, and put chemicals in the water to make it safe. They seemed to do great with that, and got pretty big in size.

Enjoy your Piranhas, they are some great fish!

Answer 4

Well, he's partially right. Bacteria need to consume somethin too...and if you let the bacteria to grow by its own, then no water change at da beginning. This is to have the bacteria to consume some waste in the aquarium. He said "since the fish are small and inside a big tank the ammonia levels won't be harmful" is not totally wrong, he got a point there. But if ammonia levels go too high, it's dangerous. A better way would be...set everything up, gravel, pump, filter...everything, and I mean EVERYTHING...except don't put in the fish yet. Go buy some bacteria(mostly in liquid form), Stress Zyme, Hagen Cycle, JBL Denitrol...just to name some. Leave it for like 2 - 4 weeks, then you introduce your fish. And another thing which you would like to be aware when introducing your fish into the tank would be the water pH...
pH testkit are available in almost all aquarium stores...they are common...