Need help with ammonia issues in a established tank

[DEE’S reef]

So my tank been set up and running since late November of 2025 and finished its cycle in the beginning to middle of December. Over the last 4 to 5 weeks I’ve been having an ammonia problem the first 2 week my ammonia was at 0.2 ppm and I did about a 10 gallon water change. And the third week I test twice a week and both times I got 0.2 for the ammonia so I did 2 10 gallon water changes. The fourth week I got zero so I thought I was good.On the 5th week I tested the first and got 0.2 on ammonia and I did a 15 gallon water change and the second time I tested later on in the week I got 0.8 for the ammonia so I did a 15 gallon water change. What do thing you could be causing this issue and what can I do to solve it.
I also went to the lfs and had them test my water and they said my ammonia was at zero and my tank parameters looked like it was just set up.

 

[D'sreef]

How are you testing for Ammonia, and are you testing for free ammonia or total ammonia?

 

[Subsea]

Sounds like your test kits are bad.

 

[Fish Fan]

Would you be using the API brand ammonia test kit by chance? That kit sometimes has a glitch where it often shows about 0.25 ppm for ammonia when the concentration is likely much lower.

I see that your tank has been running for a while, you have fish, algae, etc. There shouldn't be any reason that the tank cannot process ammonia effectively.

I wouldn't worry about it too much, I think this is likely testing error, and a low level of ammonia like that isn't really dangerous to fish, and actually beneficial to corals and macro algae.

 

[Randy Holmes-Farley Verified Community Expert]

I suspect the 0.8 ppm is a testing issue, and the 0.2 ppm rounds to none and is no concern even if real.

 

[DEE’S reef]

I’ve been using red sea test kits since January and my lfs uses API test kits

 

[Subsea]

I’ve been using red sea test kits since January and my lfs uses API test kits

OK. So both of you have compromised test kits.

 

[GoReefin]

Just curious, why are you testing for ammonia in an established reef tank? Any issues with your corals or fish that would warrant testing?

 

[DEE’S reef]

I’ve been testing for a few month to get numbers to see if my tank was stable enough for corals a I haven’t bought any corals yet

 

[Randy Holmes-Farley Verified Community Expert]

I’ve been testing for a few month to get numbers to see if my tank was stable enough for corals a I haven’t bought any corals yet

Ammonia will be fine in any tank that has had fish for months.

 

[GoReefin]

I agree with Randy. No need to test if you have happy fish

 

[exnisstech]

Sounds like you may be over thinking things. Not sure why your testing ammonia in a cycled tank. I don't even test when I'm cycling a tank but that's not the preferred method I suppose. I just watch for nitrate. I dose ammonia in cycled tanks with low nitrates.

https://www.reef2reef.com/threads/diy-ammonia-dosing-for-low-nitrate-systems.987087/

 

[DEE’S reef]

Sounds like you may be over thinking things. Not sure why your testing ammonia in a cycled tank. I don't even test when I'm cycling a tank but that's not the preferred method I suppose. I just watch for nitrate. I dose ammonia in cycled tanks with low nitrates.

https://www.reef2reef.com/threads/diy-ammonia-dosing-for-low-nitrate-systems.987087/

It’s kinda of a habit from when I was doing fresh water to make sure my tank was doing well

 

[Dan_P]

So my tank been set up and running since late November of 2025 and finished its cycle in the beginning to middle of December. Over the last 4 to 5 weeks I’ve been having an ammonia problem the first 2 week my ammonia was at 0.2 ppm and I did about a 10 gallon water change. And the third week I test twice a week and both times I got 0.2 for the ammonia so I did 2 10 gallon water changes. The fourth week I got zero so I thought I was good.On the 5th week I tested the first and got 0.2 on ammonia and I did a 15 gallon water change and the second time I tested later on in the week I got 0.8 for the ammonia so I did a 15 gallon water change. What do thing you could be causing this issue and what can I do to solve it.
I also went to the lfs and had them test my water and they said my ammonia was at zero and my tank parameters looked like it was just set up.

Salicylate test kits have a catalyst that can produce a color which results in the baseline color at zero total ammonia looking like about 0.2 ppm. Also, new saltwater can test at several tenths ppm.

The 0.8 ppm reading is far enough above the baseline to make me wonder. Off hand, I don’t have any ideas about how to fool the test to produce an erroneous 0.8 ppm reading.

How large is the aquarium or what percent of the toal volume is 15 gallons? After the 15 gallon water change, did you check to see the effect it had on the ammonia level?

 

[DEE’S reef]

It’s a 80 gallon tank with about a 20 ish gallon sump and I was doing close to 20 % water change. Cause I tested on Friday and I had that .8 for the ammonia so I did a 20% water change and yesterday I went to the lfs and they said my ammonia was zero

 

[DEE’S reef]

I might retest ammonia today to see if I messed something up originally when I tested Friday