Ammonia question in holding tank

[Vettezuki]

We are in the middle of upgrading our pond from a water garden to a proper pond. The fish have been moved to a show tank during construction.

The water temp is in the low 50s F. PH is high (cuz that's the way it s around here, about 9.0). They haven't been eating for a couple months already so there is no fecal waste. Nitrate and Nitrate are 0. NH3 is 0 (according to Seacam test) but NH4 is like 4 mg/L (total minus free, which is 0). Fish seem totally fine. Nothing obviously weird in behavior. I'm changing water in the ballpark of 15% - 25% every one to two days. There is a pump turning over that little show tank many times per hour so it must be oxygen saturated. There is a pressurized filter attached that everything is running through, but it doesn't seem to be removing any ionized ammonia.

Sooooo, is that way too high for NH4? When changing water I use Hikari Ultimate. What could I even do about it other than change like 50% water daily? Raise PH towards neutral? Messing with PH makes me nervous, but in my limited understanding ammonia has some relation with PH, like less dangerous around neutral than alkaline. But this is not the kind of thing to be guessing about.

Fish seem fine and I'd like to keep it that way.

[kevins2ooo]

Have you checked the source? The source water you are putting in could have high ammonia I think. I would dose Seachem Safe every two days or whenever you do a water change. It's hard to overdose that.

[Vettezuki]

Thanks for the idea. I checked water source and it is ammonia free. So the ammonia source seems entirely fish respiration. As stated in OP, it's already all NH4. So I guess the only thing to do is exchange more water more frequently until and unless the filter starts doing a better job.

[kevins2ooo]

I don't think you should change the water daily...at least not in large amount. That would cause too much stress to the fish.

If I was in that situation, I would do water change every other day and dose Prime / Safe. It binds with the ammonia and make it safe for the fish. Effective for 24-48 hours...by then you would just change the water and dose again.

[RichToyBox]

I would get a SeaChem Ammonia Alert Card and use it. It will tell you when you have toxic ammonia and then it is time to add more Safe. Water changes are good and as long as it doesn't change the pH significantly, or the temperature by more than a couple of degrees you should be fine doing as many as you feel comfortable doing.