hi! Lately I've had some of my swordtails die and I need some comfermation why. It started about 4 months ago when 2 of my 6 sword tails died within a week. Each one, 2 days before dying stopped eating, sat on the bottom and started breathing erratically. The next morning they would be floating dead. Now, 4 months later one of my females died the same way over the period of a week. Does anyone know why this could be? The water perameters are normal. Could it be old age? I bought the fish a year ago and they were fully grown. Any help would be great!