What the heck??? Nitrates at 120??

I do water testing on established tanks atleast once per week
last week the ammonia 0, nitrites0, nitrates 10-20ppm ph 7.2 all normal
this week ammonia 0, nitrite 0, nitrate 120??

I tested my other tanks and they are all normal 0,0, 10-20
all tanks get 20% minimum wc

tap 0,0,<10 all tanks have some live plants in them ranging from java moss to swords.


This is my 55 gal Angel tank..5 angels with 3 oto's(now 1 oto)

this tank gets scheduled 20% minimum per week this tank has swords, java moss.

yesterday when I found the high spike I did a 40% change and plan on doing a 20% change tonight.

I'm still trying ti figure out what happened :huh:

any suggestions?

the only fish that had issues were two of the three oto's I transferred from quarantine.

the angles are fine..the part that gets me is this tank was fine a week ago

so I'm going to do 20% wc everyday for a bit and see what happens.


it's got me stumped..I am checking the plants to make sure that wasn't any weird plant die off..I'll take the ac HOB off tonite and make sure there isn't anything weid there too..