Deblin2
pH of 8.6 is rare - not impossible - but rare.
I would get a second opinion or buy a new test kit.
Test kits do expire.
Again, foil sealed pouches are normally the best to use.
FasTest or Salifert are good pH test kits in my experience.
Hoping you get the new ammonia kit today - anxious to hear the readings.
Whenever you get different readings on a test kit - different back to back test readings - there's a huge cause for concern.
If you test for ammonia - and get .25 mg/L
THEN
Do another test immediately afterwards - and get .50 mg/L
Something is wrong
Either you changed something in your procedure - or the kit's bad.
Yes - It's common to show ammonia in newly mixed saltwater.
Instant Ocean - after mixing and testing it - I always test positive for ammonia-N in the new saltwater.
Readings of .2 mg/L is what I see when I mix it here.
There are ammonia/ammonium ions present in Instant Ocean, and most other synthetic sea salts. Not a lot - but they are there for sure.
Low oxygen is prevented by insuring good water circulation - especially at the tankwater surface.
Directing a powerhead flow towards the surface to get that water rippling effect almost always cures this possible problem.
Personally - I'm leaning towards overcleaning the tank, the addition of AmmoLock and bad test kits - as possible causes of your woes.
When we think something is one way - but it's really not - then all of our actions to correct may be the wrong actions.
If you had pH 8.6 and ammonia present all the time - I would imagine you'd be seeing more fish deaths too.
New test kit time me thinks