Petco Text Logo
Petco Pet Logo
  • Two Easy Ways to Start Earning Rewards!

    rewards header
    Become a member today!
    Members-only pricing and offers, personalized care notifications, Vital Care points back on every purchase and more!
    Petco Pay LogoBecome a credit card member today!

    Earn 2X Pals Rewards points at Petco
    when you use Petco Pay!

    APPLY NOW
    Learn More About Petco Pay Benefits

Why does my molly fish have black spots? Is it sick or water issues?

Updated on September 23rd, 2025

Pet's info: Fish | Unknown - Fish

Dear Sir/Mam, we have white molly as a pet and it seems to be ill since few days , It has got some kind of black spots over its body , and it seems to be increasing day by day , so we decided to keep it away from other fish to avoid spreading of disease ,the black spot to me looks like some thing is hanging on to it ,pls guide us There is no fish vet in our town ... I really need to save it ..pls doctors help me ... help the dear life plssssss......

1 Answer

Most Helpful Answer

Angel Alvarado, LVT

Answered By Angel Alvarado, LVT

Licensed Veterinary Technician

Published on September 11th, 2017

Black spots or discoloration can be caused by elevated ammonia levels. Test water chemistry using a home test kit or submit a water sample for testing. Most pet or fish stores will do this for free or for a nominal fee. Ammonia and nitrites should be 0.25 ppm (parts per million) or less, nitrates can be 40ppm or less. Partial water chnages daily should be done to decrease ammonia levels. Use only aged or conditioned water that is temperature matched to prevent further stress or shock.
Elevated ammonia levels can be caused by overfeeding, new tank syndrome or overstocking.
Vote Icon1Pet Parents found this answer helpful

Smart Picks for Smart Questions

Have A Vet Question?

Book an appointment with the pros – our expert vets are here to help.

Share

Styled arrow button