I have had a 5 gallon tank cycling for about 3 weeks with no fish in it. I would use janitorial ammonia to feed the Safestart Plus bacteria that I put in the tank and then each day I put in a little bit more ammonia as I read to do on many sites on the internet. Anyway, at last, I thought my tank had cycled as one day it read as 0 ammonia, o nitrites and 10 nitrates. I was ecstatic and went and got my new fish, which was one betta fish. He has been happily swimming in his new tank for 3 days. I have an ammonia alert card in the tank and it says there is no ammonia so I did not check any levels. But today I decided to check using the API master test kit. It read as .25 ppm ammonia and 1 ppm of nitrite and I was shocked. Since I have been putting Safestart Plus in my tank each time I would do a water change and actually put in a whole bottle when I set the tank up I can not understand why I have nitrite readings at all. So I did a water change, about 50%. But then I made a big mistake and tested immediately afterward and it still read 1 ppm of nitrite even though I took out half the water. Then I did another water change, about another 50% and measured again and the nitrite went down to .25 ppm. So I left it there and added more Safestart. After that I read on this forum that you are not supposed to test immediately after doing a water change so I am scared for my poor little betta who still is swimming happily around. My question is, if the tank had cycled before I put my betta fish in, why did the tank have nitrites in it and what can I do about it without doing multiple water changes in one day. I also did test the water I added, which was a combination of spring water, treated tap water and RO water. None of them had nitrite in them. Please help.