Nitrates and Ammonia Problem

The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.


Aquarium Advice Apprentice
Jul 3, 2019
Keelung, Taiwan
Hello. I have a 15 gallon tank and I'm having a massive problem with extremely high nitrate levels (over 250mg/L). Currently, my tank runs at about 25-30°C with it being summer here, I have a fan cooler running. I currently have 3 platys, 2 danios, 3 snails and a plec in my tank. I have about 5 or 6 plants too. I had about 7 platys and 6 danios before but they all started dying. I tested the water and noticed very high ammonia levels (5mg/L) so I started treating for that with Ammosafe and the current ammonia level is 0.25mg/L. I do 20% water changes about 3 times a week but it hasn't made the slightest dent in the nitrate levels. I just use filter sponge in my filtration system and I cleaned out the whole filtration system about a month ago. My tank has been established for more than 3 years and I've never had this problem before.


  • IMG20230813174818.jpg
    227 KB · Views: 17
  • IMG20230813174850.jpg
    252.6 KB · Views: 15
  • IMG20230813174801.jpg
    204.4 KB · Views: 15
  • IMG20230813174652.jpg
    150.4 KB · Views: 14
  • IMG20230813174630.jpg
    161.2 KB · Views: 15
Check your water supply for ammonia, nitrite and nitrate.

If the tap water (water supply) doesn't have any ammonia, nitrite or nitrate, then do 75% water changes and gravel clean the substrate every day until the levels are 0ppm.

If the tap water has nitrates, depending on what level it is, you might need to find a new water supply.

If you do have high nitrates (above 50ppm) in the tap water, then contact the water company, the state government, and the health department and let them know, because nitrates are poisonous to people, animals, birds, reptiles and fish and the water should not have any. If the government departments don't do anything, contact the press and get them to do a story on toxic tap water. That usually gets the government moving and fixing the problem.


You shouldn't need a cooler on the tank unless the water temperature regularly goes above 30C. My tanks used to sit on 30-32C right through summer and the fish were fine. I had airstones bubbling away and the fish didn't have any issues with the warmer water. In winter I set the heaters on 18-20C and the fish had a cool period.
Thank you very much for the advice ... I tested the source water and it's all normal. Been suctioning the gravel but I think my suction tool is too small so I'm going to go buy a bigger one. Touch wood, no more deaths, but my one platy doesn't look so great.
Top Bottom