Fish are dying! Help!

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Damiri

Aquarium Advice Apprentice
Joined
Mar 20, 2017
Messages
17
120 gal tank with plants, cories, platys, mollies, barbs and gouramis. Everything seemed fine until a couple of days ago when i found a barb has died. We have been testing for ammonia and nitrites regularly and both are at 0. Between yesterday and this morning we have lost a gourami, a catfish and 4 cories. I just retested water and the results are:

Ph 7.1
Ammonia 0
Nitrite 0
Nitrate 160
We have a CO2 supplementation to liwer the ph because our water is naturally at above 8

Obviously nitrates are astronomical which surprised me but could that be killing the fish? It explains the algae problems we've had lately. I am doing a 50% water change right now but is there anything else i can do? I am surprised the cories died but not mollies. They are so hardy.
 
Wow I have never seen nitrates that high. You might want to do 50% today, 50% tomorrow. Clean the substrate and your filter too. Try to get it down to 40.
 
Wow I have never seen nitrates that high. You might want to do 50% today, 50% tomorrow. Clean the substrate and your filter too. Try to get it down to 40.
+1 high nitrates can be toxic, above 40 most do a water change.
 
Thank you. I vacuumed the substrate and changed about 50% of water. I will do another water change tomorrow and the day after. In the meantime we lost a young pleco and a swordtail. I hope there will be no more casualties. I had no idea the nitrate levels can climb so fast. The last time i checked was about 2 months ago or so and it was around 10-20 then. Lesson learned.
 
I builds as the waste in the tank does. If you have plants they use a good amount. I usually test at least once a month and feed lightly to keep it in check.
 
You can plant Pothos to grow out of an HOB or just submerge the roots. They love to suck up Nitrates.

But def, water changes for now. [emoji51]
 
Last edited:
so after a cleanup, filter cleaning and 3 water changes i got nitrates down to about 40-80 (hard to tell, the colors are so similar). Still higher than they should be but much better. I lost one more fish but now the rest are behaving much more like normal. They are not as lethargic, especially the cories. They used to mostly just rest at the bottom and now they are scavenging again. I put two more plants into the tank and will feed the fish a little less. I might have been overfeeding the crowd... I guess i should do another water change as well...
 
Do you only swish your filter media (pad,cartridge, or ceramics) in the water you just siphoned out when doing a water change. If not you can destroy your beneficial bacteria or you could be throwing it away.
 
I just rinsed the gunk out of the media in the water taken from the tank. Basically I just swished it around in a big bowl of tank water and put them back.
 
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