Help please algae issues

[Coralgurl]

I know its been covered many times so if someone could point me to some good reading material on phosphates and nitrates and how to deal with it.

I've been doing water changes to reduce both, added a skimmer to help remove nutients, manually removing hair algae and reduced feedings. I've lost a number of corals like a frogspawn, octospawn, mushrooms have bleached and a brain coral has tissue receding. I only have api tests for phosphates and nitrates, tested both and they are high (not home at the moment and can post later).

Fish are fine(I have 2 clowns, 2 chromis, flameback angel and flame hawfish), think all my snails are dead as I haven't really seen them. And my awesome nem is not extending its tentacles like it did a few weeks ago.

Tank is running with a canister filter that is cleaned thoroughly every 2 weeks, I've recently switched to enheim bio media, and have carbon and gfo in it.

Any suggestions on how to turn this around?