Check your nitrates.
Bringing established media, gunk, decorations, etc. means that you are likely bringing the same ratio of A-bacs and N-bacs, as you need to process ammonia and nitrite. (A grossly misrepresentative set of numbers... let's say that to process 1 ppm ammonia to nitrate requires 10 million A-bacs, and 20 million N-bacs... then your additions may have had a 1:2 A-bac to N-bac ratio and as a result, each 0.1ppm ammonia that is processed each 24 hours to nitrite is also 'immediately' processed to nitrate.)
So, whatever the A-bacs process, might also be processing the nitrite produced immediately, so you don't see the nitrite. If your nitrate is rising (although its not a very reliable test for specific numbers) it indicates that's the case.
Either way, you are still looking for the same end point - ammonia being fully processed within 24 hours, from ammonia to nitrate.
It appears that your current set-up is processing somewhere in the neighborhood of 0.5-1 ppm per day of ammonia.
Let's say July 12 was about 3.5 ppm.
July 14 was closer to 2 ppm than 1ppm.
(That means that you processed about 1.5 ppm in 2 days, roughly 0.75 ppm per day.)
Added ammonia back to 3 ppm, but possibly a bit higher again.
July 17 about 1ppm, maybe 1.5.
July 18 about 0.5 ppm.
So, in the 3 days between July 14 and 18, you processed about 2.5 ppm, roughly 0.8ppm per day... give or take.
The odd part about that is that generally, the bacteria will roughly double every 24 hours... BUT, moving from one tank to another can impact that and disrupt their biofilms a bit, so it could be a bit slower for a while.
Keep updating and we can confirm where this is heading. I'd add a snack dose of 1ppm now and check again in 24 hours.
Bringing established media, gunk, decorations, etc. means that you are likely bringing the same ratio of A-bacs and N-bacs, as you need to process ammonia and nitrite. (A grossly misrepresentative set of numbers... let's say that to process 1 ppm ammonia to nitrate requires 10 million A-bacs, and 20 million N-bacs... then your additions may have had a 1:2 A-bac to N-bac ratio and as a result, each 0.1ppm ammonia that is processed each 24 hours to nitrite is also 'immediately' processed to nitrate.)
So, whatever the A-bacs process, might also be processing the nitrite produced immediately, so you don't see the nitrite. If your nitrate is rising (although its not a very reliable test for specific numbers) it indicates that's the case.
Either way, you are still looking for the same end point - ammonia being fully processed within 24 hours, from ammonia to nitrate.
It appears that your current set-up is processing somewhere in the neighborhood of 0.5-1 ppm per day of ammonia.
Let's say July 12 was about 3.5 ppm.
July 14 was closer to 2 ppm than 1ppm.
(That means that you processed about 1.5 ppm in 2 days, roughly 0.75 ppm per day.)
Added ammonia back to 3 ppm, but possibly a bit higher again.
July 17 about 1ppm, maybe 1.5.
July 18 about 0.5 ppm.
So, in the 3 days between July 14 and 18, you processed about 2.5 ppm, roughly 0.8ppm per day... give or take.
The odd part about that is that generally, the bacteria will roughly double every 24 hours... BUT, moving from one tank to another can impact that and disrupt their biofilms a bit, so it could be a bit slower for a while.
Keep updating and we can confirm where this is heading. I'd add a snack dose of 1ppm now and check again in 24 hours.