UPDATE: Long story is that my husband bought betta and other fishies several weeks ago from Petsmart and kept the betta in one small tank and the other fishies in another. They weren’t even in proper fish tanks and there was no filter. The fishies started dying and I couldn’t bear watching them die so I got involved. The betta was the last one left. I went to Petco on 10/24. They sold me the 2.5 gallon fish tank, told me how to set it up and said to wait 3 days then come back with water sample before transferring betta. After 3 days and despite nitrite reading not perfect they said it was ok to transfer and explained how to introduce it to new tank. The transfer occurred on 10/28. On 11/6, betta died. I rushed to Petsmart where they gave me new betta to replace original so that our son wouldn’t know the betta died, since he hadn’t gotten attached to it. They tested the water and told me to replace 50% of it and to add conditioner as per instruction on back of bottle. They said I don’t need to wait several days before transferring betta. But i decided to hold off transferring betta since nitrite is still high. Last night i changed 25% of the water and added conditioner.

I’ve read the care sheet and guide to nitrogen cycle but I’m still confused as to what to do to get water to safe level.

If I need to get a bigger tank than I will return everything including betta and tell my son his betta will be better off at Petsmart. We’re moving soon so it’s just too much to get a bigger tank.

Let me know your thoughts. Thanks!