Ive noticed over the past few days that some fish were gasping at top . I tried turning up the oxygen pipe and then the next day they started again so i treated the water with aquasfafe and did a 25 % water change . today they started again so i did another 25% water change . but now ten mins later i have a fantail floating upside down at the top gasping what can i do ?? all water p[erameters are normal . whats going on i've just added a dose of swimbladder treatment 