Problem with corals

[1bigstud]

Im not sure what the problem could is, but the last few times I have tried adding hardy softies (ie xenia, colt) they started melting away after a day,
my salinity is a bit low(1.025)
everything else checks out except for phosphates.
so I have no idea what else the problem could be.
I did have an algae out break, but added some macro did some scrubbing and water changes, the nuisance algae is almost non visible in the tank.
I do have a reddish pink algae growing on the sand bed/glass
I am open to suggestions/diagnosis and advice.
One day I would like to have corals in my tank.
It is a 75 gallon tank.
33 gallon sump.
becket skimmer powered by a mag 12.
main return is a mag 7
strong current in the tank, roughly 120lbs of live rock in the system.
live stock.
flame hawk, scooter blenny, regal tang, green chromis.
atleast 1 hermit crab, baby starfish which must have spawned off one I bought some time ago. 1 reddish green mushroom.