Need Help High Nitrites

[Educatedthug]

Ok I have a 155 gallon tank
wet dry filter.
rena xp4
magnum 350 canitser

my ammonia is 0ppm
my nitrate is between 0 and 5.0 ppm cant really tell with test colors
and nitrites are between 0.50 and 1.0 ppm

I have
4 tiger barbs
5 cgouramis
2 loaches
1 betta
all get along fine
4 days ago my nitrites where at 3.0 maybe 4.0 i did a 75 gallon water change. Nitrites at .50ppm 2 hours after water change
this would be 3 days ago
checked again in the morning and they where up to 1.0 again in morning came home from work 7 hours later and back at 3.0 to 4.0 changed 120 so gallons of water tested the tap water water fron the python all nitrites at 0..
checked water in tank 0.25 ppm
2 days ago my wife tested water and 3.0 and added something called Kordon AmQuel+ Plus. she got from petco saying this would work she read directions and added 80 mil for 155 gallons plust the 30 gallons of filter water. it killed the angel fish that i hadbecause it lowers the oxygen in the tank i would not have thought about the filter water but anyway it lowered it lowered the nitrites to 0 ppm
ok this afternoon I check the nitrites and they are back up to 1.0 ppm what is going on here
what else can i do i dont think i over feed the fish a little pinch of food turn filters off so it does not get sucked up
please help:bowing:

 

[Jaysn]

How long has the tank been set up?

 

[Educatedthug]

I did a fishless cycle that finished 4 weeks ago then put minos in tank to keep bacteria then added 3 fish a week with no problems had a puffer that was moved to a brakish tank and a gold fish that was also moved to another tank

 

[TKOS]

So you have some sort of mini cycle happening. It can happen. Just do water changes to get the nitrite lower than 0.25 ppm and you will be fine (you will have to test every other day to make sure they aren''t creeping back up). Since you have a large tank that may be hard to accomplish at first so adding 1 tsp of NaCl (salt) per gallon of water (added to fresh makeup water) will help combat the toxic effects of nitrite in the short term.