If you are replacing trace elements with weekly water changes, your calcium level is going to be closer to high 300's to low 400's, depending on your salt mix.
Salifert and Elos make much better test kits. They are more expensive though. All that said, low, or high calcium won't kill fish.
Ammonia will need to be processed. I'm thinking it's because you added 10 fish in a months time. Your beneficial bacteria colony will have to catch up to your current bio load. until then, you'll see ammonia. how much and how often are you feeding?
Cut back on that IMO
. That's contributing to it.
As for Reef Crystals, that's completely untrue. It's a fine salt to use, along with most of the others.
If you don't have corals at the moment, don't even bother testing for calcium, alkalinity, or mag. Just test for ammonia, nitrite, and nitrate.
You should have zero ammonia and nitrite, and lower nitrate (I would like to see it below 10-20ppm).