I set a 60 litre tank up and run it for 3 weeks, all water parameter levels fine. Added 4 fish, left 4 week's all fine. Added 4 fish again and 5 days later fish started to die. Checked levels and the nitrite and nitrate were totally soaring. After first fish died on Saturday I did a gravel vacuum, large water change. Same again Sunday after another 2 fish died, also added Seachem Prime to try and save the fish.

Did another water change and vacuum today, still super high levels. I have 4 fish left and they are obviously struggling. I don't know what else I can do to help the poor things. I'm not very experienced with these problems, never had issues in the past.

Anything else I can do to help the poor fish? I feel so cruel 😥

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    Hi Lisa and welcome to Pets, how were you cycling your tank for those first 3 weeks? I assume you did fishless cycling, were you feeding the empty tank with fish food or were you using pure ammonium hydroxide or ammonium salts, or else? As I understand, there is only problem with high nitrite and nitrate, but ammonia levels are safe, am I correct? What types of fish were/are those you had added and how big they are?
    – lila
    Oct 19, 2020 at 20:38
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    I was using the ammonium hydroxide as was recommended to me,I wasn't sure at the time. All other levels are good and stable yes. I added platys/ mollies 4 in total and they were fine. After that I added 4 guppies and then it all seemed to go wrong
    – Lisa
    Oct 20, 2020 at 6:12
  • Okay thanks for response; please don't feel cruel Lisa, fish are deceivingly difficult animals to take care of and it's not your fault that this happened, I think that just the fact that you know what fishless cycling is and that you used a "clean" method with ammonium hydroxide to cycle your tank shows that you are more knowledgeable than many people that tried fishkeeping.
    – lila
    Oct 20, 2020 at 20:05

2 Answers 2


The first thing you need to do is to add some aquarium salt, this is done to counteract the effect of the nitrite on your fish' gills.

The aquarium salt concentration to use is 0,3%.

Do water changes 20% each day until the nitrite level drops, cut down on the feeding of your fish so you only feed twice a week and only a little food each time (this is to lower the bioload in your tank).

Do not clean the filter until you can see the flow is reduced, but keep on vacuuming the gravel each time you change some of the water.

Do not worry about the nitrate for now; you will have time to lower it when the nitrite spike is over in a couple of weeks.

More information about cycling a tank can be found here.


So, you could try putting in duckweed or water lettuce, they grow rapidly, and various websites recommend it (So as youtubers) as they grow rapidly and use nitrates to grow, The nitrate levels should go down rather quickly.

You might be over-feeding too, nitrate levels rise if there is uneaten food in the tank, you might want to add a catfish of some kind to clean the waste food and prevent the nitrate levels to soar high again.

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