Zenia Melting!!!

[reefy]

I don’t know what is going on with my zenia, it starting to melt, I had it for around tree months; 1 month was pulsing but wasn’t as healthy as the first 3 days(skinny and brown) two months after it started to shrink and yesterday it started to melt. I thought my iodine was low so then I start adding 15ml once in a while (1 dose every 4th dayish) anyways my parameter of my tank is: PH: 8.2 Temp: 78-82 NO3: 5-10 salinity: 0.025-0.026. calcium: 550. I think my Parameter is pretty descent isn’t? so why the hek they are melting!!!! Any idea? Oh yeah I tried to place him on a low flow area but I don’t know how about the lighting, I have 2X400watt Metal hilide….. please help....Thanks in advance