Sudden spike of Ammonia in 120 gallon

[Shell Script]

2 months ago I started my 120 gallon reef tank. The Tank cycled in 3 weeks, but I didn't add fish till a month ago. 5 days ago I added my clown and blenny to the 120 and the ammonia and nitrite read zero until today. Ammonia and nitrite currently read around 0.25 (slightly less), I did use a API test kit, but I used one with my last tank and it served me well. As of now i've done a 10 gallon water change, and i'm currently mixing more water for a larger water change. Ive also added some fritz 9 left over from the cycle to help build more beneficial bacteria . I'm confused how my water parameters changed so quickly because i've found nothing dead. I'm also looking for tips on how to save the tank. thanks.

Current inhabitants:
2x damsel fish
1x clownfish
1x Lawnmower blenny

1x Xenia frag
1x GSP frag

3x nassarius snail
3x halloween hermits
1x blue legged hermit
3x nerite snails
1x Very large turbo snail
2x astraea snails

Notes: all of my livestock are currently alive so it's not them. Could my problem be improper filtration? I feed mysis, brine, or flakes once or twice a day, usually leaving 12 or so pieces of food to fall for the inverts. I use a sock, media balls, carbon, sponge for regular filtration and have ran a Comline DOC 9012 (protein skimmer/150 gallon medium bioload) for 2 days. In my 120 I have 2 rocks from my previous tank with hair algae for my blenny to eat. Could it be algae die off? yesterday before the spike i added a jar of copepods from algae barn, so i called them to see if they could've caused the spike and they said no. That's all i could think of in terms of what started the spike.

 

[fishywishy]

It’s probably just the test kit, api test kits haven’t been very accurate for me.

 

[Reefering1]

 

[mihali]

2 months ago I started my 120 gallon reef tank. The Tank cycled in 3 weeks, but I didn't add fish till a month ago. 5 days ago I added my clown and blenny to the 120 and the ammonia and nitrite read zero until today. Ammonia and nitrite currently read around 0.25 (slightly less), I did use a API test kit, but I used one with my last tank and it served me well. As of now i've done a 10 gallon water change, and i'm currently mixing more water for a larger water change. Ive also added some fritz 9 left over from the cycle to help build more beneficial bacteria . I'm confused how my water parameters changed so quickly because i've found nothing dead. I'm also looking for tips on how to save the tank. thanks.

Current inhabitants:
2x damsel fish
1x clownfish
1x Lawnmower blenny

1x Xenia frag
1x GSP frag

3x nassarius snail
3x halloween hermits
1x blue legged hermit
3x nerite snails
1x Very large turbo snail
2x astraea snails

Notes: all of my livestock are currently alive so it's not them. Could my problem be improper filtration? I feed mysis, brine, or flakes once or twice a day, usually leaving 12 or so pieces of food to fall for the inverts. I use a sock, media balls, carbon, sponge for regular filtration and have ran a Comline DOC 9012 (protein skimmer/150 gallon medium bioload) for 2 days. In my 120 I have 2 rocks from my previous tank with hair algae for my blenny to eat. Could it be algae die off? yesterday before the spike i added a jar of copepods from algae barn, so i called them to see if they could've caused the spike and they said no. That's all i could think of in terms of what started the spike.

That is a lot of inhabitants for a tank that is just about two months old I would not add any more life for about a month just to let the bacteria grow a bit more that could’ve been why the ammonia spiked

 

[GARRIGA]

Cycled tank should never see ammonia therefore possible reagent has expired. If using API, their test strips are accurate and I've verified using my own reference sample. However, if nitrites also now elevated then perhaps something did go wrong although check on expiration of that reagent as well. Why I always have two separate test kits so I can validate one against the other.

 

[GARRIGA]

Seachem ammonia badge worth having as a constant watch dog as those tend to be accurate although need to be replaced as needed. Cheap insurance for something that should never occur in a cycled tank.

 

[exnisstech]

TBO I've never tested ammonia after a cycle. Actually I don't even test it durring the cycle any longer. Not a recommendation but once I see nitrates I start slowly moving forward.