SOS. What’s wrong with my fish? My female platies have both been favouring sitting on the bottom all day and we did a water change with some prime and parameters were okay and now my guppy is breathing very fast also
Looks like Nitrite or amonia poisoning. If the pH is 7.5 or higher those two readings are toxic. Add a second filter, dump a bottle of safe start plus in it and please stop using filter cartridges if you’re indeed using them.