I'm currently cycling tank with a few fish Have a wee bit of ammonia which I used ammo lock to de-toxify been going like this for six weeks but I have got up this morning and fish are at the top of the tank, tested the water and I now nitrite which I am happy about as it means my cycle is on its best stage, I done 40% water change to bring the levels down so that my fish are happy again but I re tested the water and now I have no nitrite! Is this bad???