About a week ago I set up a 5 gallon for my betta and it appears to have cycled well using half the filter sponge from my 10 gallon. Two days after setting it up it read 0 ammonia, 0 nitrite, and 5ppm nitrate. However, a week later it reads everything the same except nitrate is 0. Is this normal? If it’s this clean, is it safe for me to do a 50% water change every 2 weeks?