Why can't I keep softies happy and alive

[bullitr]

I have a 435 gallon mixed SPS tank
All of my SPS are growing well.
But I can't keep Xenia ever since and all of my neon green leather finger are shrinking and most likely died like the one before.
I feed really heavy 40 cc -50 cc per day but I used to have a skimmer rated for 1600 Gallon so I downsized to reef orca 250 pro with dart gold and still can't keep them more than a week.

Also marco algae died in the tank too.
I don't do water change since Jan 2009

I have mushroom and toadstool leather too but it's not growing but it's alive.
Any thought?

 

[slapshot]

I would suspect lack of iodine and or iron. Macros dying is the clue. Especially if your SPS are doing fine as they need neither.

 

[Nanook]

I would consider starting water changes.

 

[Misled]

I would consider starting water changes.

I agree. There's lots of trace elements that most likely have been all but eliminated from your tank. It may not effect some things, like your SPS, but it's effecting the softies.

Water changes aren't just for removing things from the water column, it's also for replacing things we don't have the ability to test for.

 

[judgedread]

i have had the exact problem you are facing.

it is due to low DOC dissolved organic content.

in a low nutrient tank with zero po4 and no nitrate my leather finger corals die and also
my blue xenia.

yet my pink pom pom xenia does just fine. go figure.