The API tests are ok. Not the best quality- but for these three should be ok. As you progress in the hobby it’s worth picking up some better quality tests. Here is what I test on a weekly basis:
Temp (I have three checks: heater control, chiller and a hand held laser pointer kind), salinity (I use refractometer), alkalinity (Hanna checker), magnesium (salifert brand test), calcium(Salifert brand test), PH(cheapo handheld teater- api twat as back up) Phosphates (Hanna checker), Nitrates (Salifert brand test). Once your past cycle ammonia and nitrite should remain at or close to zero. I don’t test those two as often as I test the others.
Looks to me like your still cycling. When you see nitrite spike and then get to 0 you should be cycled. Looks like your in the nitrite spike, should not be too much Longer.
I would remove the fish, test daily util you see nitrite at zero.
Couldn’t hurt to add more “bacteria in a bottle” like quick start or something like that. But I think either way your in the middle - towards the end of your cycle.
Once cycled start with one or two cheap hardy fish. (Would advise against damsel fish)
you could do freshwater mollies but need to do 6 hr slow acclimation to salinity and temp. Molly’s are cheap and are algea eaters. Even freshwater guppies can be acclimated to salt water. But again: At lease 6hr acclimation- or longer. Some do it over days or weeks. I’ve had luck with 6hrs.
Hope this helps.
HAPPY REEFING!