set up a mature water tank but the nitrite is off the chart ? help

Question
Hi i hope you can help because i really dont understand what is going wrong.  Firstly there are no fish in tank so it is not a life or death question.

i have two 150 litre tanks both set up and cycled by myself and never had a problem with either of them and luckly (touchwood) not even from fish diseases. I bought some guppies (rabbits of the fish world) a while back and was getting sick of the fry being eatten in the main tank plus i am getting some nice colouered males now too ( they look nothing like the ones you can buy in shops) so what to breed them if i can. i picked up a small second hand 30 litre tank for the job and cleaned it all out properly b4 i started.

The problem i have got is i used the water out of the main tank i have got the guppies in and have left it to cycle (like i did with my other tanks) i tested the main the tank water ,PH ammonia and nitrite, before adding to the breeding tank and it was as it should be added the water and tested a week later and the ammonia and nitrite had raised a little. I left it another week and it was still the same so did a 30ish% water change tested the water againa week later and the ammonia had dropped slightly but now the nitrite is off the chart and i am unsure to what is wrong or this is normal ? As i have never set up a tank using mature water before.

I will say the filter was new when put in the breeding tank and stupidly didnt add it to the main tank to cycle as i had it months before i bought the breeding tank. Is that what might be causing the problem ? There is gravel and orniments and plants in the tank but havent added chemicals to the water due to it being mature water plus to be honest i dont like using them either

I hope you can help me understand this one as i am clueless now to what has gone wrong and i am on the verge of giving up and doing 100% water change

Thanks
Andy

Answer
any time anything new is added to an established aquarium it will change water parameters. in this case the water was added to a new tank with a new filter. So the mature water now has nothing to keep the good bacteria alive and it dies. So basically everything restarts. If you have a cured piece of foam from your established aquarium, put in in the filter on the breeding tank this should help the process. otherwise you will have to add start right or cycle, to keep the water going. you can find it at any pet store. Every aquarium has a natural slime coat on the glass that is a sign of a good aquarium, take this slime coat away and the whole balance is messed up. that's what is wrong with your tank you added mature water to a tank that had no slime coat and no bio..




Hope this helps.