1. Poor Water Quality: Check other water parameters like ammonia, nitrite, and nitrate levels. Even if the pH and temperature are ideal, high levels of these compounds can be harmful to guppies.
2. Sudden Changes in Water Parameters: Ensure that you're not making rapid changes to the water conditions, such as sudden pH adjustments or temperature fluctuations. Guppies are sensitive to sudden changes and can become stressed or even die.
3. Disease or Infection: Examine the guppies for any signs of disease, such as white spots, body sores, or unusual swimming behavior. If you suspect an infection, isolate affected guppies and treat accordingly.
4. Overcrowding: Guppies require enough swimming space. Overcrowding can cause stress, competition for food and resources, and reduced water quality, leading to health problems and death.
5. Incompatible Tankmates: Ensure that the guppies are not kept with aggressive or incompatible fish species that might bully, injure, or stress them.
6. Nutritional Deficiencies: Make sure the guppies are receiving a balanced diet that includes both live and commercial foods appropriate for their size. A lack of nutrients can weaken the immune system and make them more susceptible to disease.
7. Genetics and Inbreeding: If the guppies are from the same genetic line or have been inbred, they may be more prone to health problems due to decreased genetic diversity.
8. Toxic Substances: Check for the presence of any harmful chemicals or toxins in the water, such as residues from pesticides or cleaning agents, which can be toxic to guppies.
If you've ruled out these factors and the guppies are still dying, it's best to consult with an experienced aquarist or veterinarian specializing in fish health to get a proper diagnosis and appropriate treatment.