Hey guys! My previous betta passed away last week and i decided to get another one. Im using the same tank. It is a 9L heated (around 27 degrees celcius) and filtered tank with no live plants. Just a little ornament. When my last betta died i cleaned the gravel and the whole tank and started fresh. But i made sure to clean the filter with the old tank water bcoz i didnt want to lose any good bacteria. However i tested my parameters and the ammonia was high the first day or so. The next day my ammonia went down to 0.25ppm and now my nitrite and nitrate levels are very high. I did a 20% water change but nothing has changed. My fish is active and does not seem to be bothered by the levels. My nitrite is at 5.0ppm and my nitrate is between 20 and 40ppm. Any suggestions on what to do?