wisdom please

[newtofish]

I have adopted a 20 gallon reef plus fish tank. I have had it for a month. It was established for nine months previously adn we moved everything in water so nothing died at first. It has one occelaris? clown, two sand sifting gobies, Lenny the Blenny, two shrimp adn a crab. It had three snails when I got it adn about 25 aiptasia about the size of a dime. For coral it has a red donut coral, a brain, two trumpets, green star polyp, a few mushrooms, two plates and xenia.

After reading I began to attack the aiptasia with boiling water and a syringe and over a course of three weeks they are gone. The tank was covered in hair algae on all the rock. It has two powerheads, skimmer, filter adn hagen t5 lights. I have done three fairly large water changes and my nitrates, nitrites, amonia are undetectable. My pH was initially low but I have added some trace supplement and that seems normal now. My green plate coral and snails have died, and my orange plate that has been super happy, eating mysis shrimp has just lost its mouth? this morning. It looked great yesterday and the color is all gone in the center and it looks dead (it isnt sending out 'feelers'). Is it?

Also my trumpets heads are starting to fall off adn the hair algae is overtaking them. Why are their heads falling off? Will they grow back? I have added phosban to my filter media and manually removed much of the hair algae but the trumpets seem doomed to die!

Oh and I feed rinsed frozen mysis shrimp twice a week and some dried krill on other days.

What am I doing wrong? Any suggestions?

Thanks!