If salinity (SG) is 1.022 you can bring up to 1.023 next time you do a water change during your maintenance schedule.
The rest of params are fine.
I think you should make sure the system is stable and keep things running that way.
Make sure your Ca is around 380 - 420ppm.
Alk is great like that.
Keep an eye on your light.
Your system has algae and Cyanos? It's the water chemistry/light. That's why they told you to put carbon in the sump.
Excess of organics and too much light. The two are not balanced out.
You're probably feeding too much "junk food", or waaaaay too much " good food" and not doing enough water changes too.
The reason the zoas are melting could have little or nothing to do with the above observations. To fix the problems seen is a good start.
Oh, one more thing...
The Instant Ocean is not like many years ago. It's quality has dropped!!! Many people are saying that.
I'm using Red Sea now, instead Instant Ocean, after years.
If you had success with H2Ocean Pro + you should stick with it, I guess. Hopefully others will come to tell more about the salts.
Also, forget Purple Up!! It doesn't really do anything for the coralline algae in the long run. Many have also reported that. It's not a magical portion.