We have gone through so many guppies and I just don't understand. The tank is cycled. These are the stats... 10 gallon heavily planted +1cave(fake plants) ammonia:0 nitrite: 0 nitrate: 20 Ph: 6.8 (it is naturally very very ,low but we add small amounts of stabilizer dissolved in water changes to keep it steadily almost neutral. Otherwise it would be like 5.2.) temp:78-82 usually 80. 1 male guppy, 2 females and another dying female(isolated), about 20-30 fry of different ages. All belonging to the dying female. How it happens is with females they gasp at the surface with a bent spine as if they were trying to escape the water(the tank has lots of oxygen. There's a large airstone and a strong filter.) and then they cant swim anymore and sink to the bottom where they flit around in an attempt to swim until they die. With males it usually starts with swimming against the current and shaking/bending their tail as if trembling in fear and then they hide somewhere and die overnight. Does anyone have any idea what this is? There are no signs of sickness other than not being able to swim and a bent spine in the last hours. (she does have 2 tiny red spots iv never seen before though, possibly scratches from attempting to swim face first/sideways into the gravel.