Starting New Tank From Existing Tank Without Cycling?

[Lobster.Lounge]

So, for those who remember, i had originally planned to have an exodon tank. aside from the lacking quality of the exodon at big als, when i purchased 7 sterbai cory, i fell in love. forcing me to buy 7 more. my new tank stock list is as follows.

2x Kribensis (breeding pair)
10x red eye tetra
10x rummynose tetra
10x cardinal tetra
14x sterbai cory

basically i will be breeding the kribs in the 55 gal community. but would also like to breed the cory so id like to start a smaller, 20 gal or so to breed the cory, and as well to house the krib fry once theyre big enough to leave their parents. i was just curious, if i were to put water from my existing tank into the new one, then take the HOB filter from my 55 gal and put it on the smaller tank (i have 2 on the 55, i would then buy a new one for the 55) would i be able to get away without cycling? essentially the filter and water is completely fine to stock right away isnt it? i could be wrong, but need the experts!

 

[waterdrop]

It depends on the timing of the various things. I can't tell which of your listed fish are part of a plan and which have been in the 55g already and for how long. If the two HOB filters have been running together all along and it's been enough time, they will be probably fairly balanced in their bacterial populations (and the media are the same we presume.) Therefor if the only fish they are taking care of are the 14 cories, then the moved filter would only theoretically handle half of them, but if the cories are a minority of the bioload the filters are handling then one of the filters might handle them right off (the water is immaterial.)

There's a better way. What you do is very similar to a mini-fishless-cycle. You set up the new tank and move one filter (of course, you then should be prepared to do water changes on your main tank if necessary and be testing perhaps every 12 hours) and dose the new tank to 5ppm with household ammonia (just like you did in your fishless cycle) and then you simply perform a "qualifying week" where you see if the filter can drop 5ppm ammonia to zero ppm ammonia and zero ppm nitrite within 12 hours each day for 7 days (this is the basic definition of a working biofilter, which presumably yours is if it's a fully cycled filter.) This ensures there are no mistakes. However, if you feel the biomass of the cories is very close to half of your total biomass then the plan to split the fish and simply be ready to perform fish-in-cycle type water changes might work out ok.

~~waterdrop~~