I added bio spara and full load of fish sunday and have lost 3 of my six serpe tetra. One monday,one tuesday, one today. I checked water every day and today is first day ammonia at.25, PH 7.6, nitrates 0. At a loss as to why fish have died no signs of anything till swimming on sides and floatiing. Feeding tropical fish flakes and all seem to eat well? is it time for water change? how much?tested now PH 7.6 - nitrates 0 - nitrites 0 - ammonia .25. Do you think bio spira not working and do I need more. Put in 3 oz package? water change 50% ?