Please help, we started our 27 litre tank 10 weeks ago. .After 2 weeks we bought a betta. He has been fine. Doing daily water changes, checking water etc. No3 is 10, no trace of NO2 or amonia, GH is 16, KH3, PH 6.8, Chlorine 0. 6 weeks after Bubbles we introduced a Cory Dora, all fine...