Large sps colony dying from the bottom?
 

I have a huge birdsnest colony smack dab in the middle of my tank. Its Gotta be 3 years old and has grown from a tiny frag to the monster it is today. So last week I notice some white at the base but didn't think much of it. Now, entire branches are dying off over night. Its happening fast! I've clipped off the dead stuff to try and prevent spreading but anyone know what could cause this weird shift?

Only factor in my tank that's changed is I've pulled 5 fish to reduce bioload and have water changed my tank aggressively for maybe 2 months to bring my nitrates from 10 down to 5. I was changing 20% weekly.

Could it be a pest attacking?

Parameters

Phos - 0
Nitrate - 5
Cal - 450
Alk 10.2
Temp 80

Everything else in the tank, my acros, monti, lps, zoas, everything is totally fine, its just this one big birdsnest...

From what I've read it seems most corals like some nitrate in the tank.

It could just be yours was adapted to your levels and it changed to rapidly for it to deal with once you removed the fish and did the water change.

Or so I suppose

Ya I agree and I do still have a reading of 5 so there is some in there. I thought at first maybe the reduction was the issue but I reduced the nitrates over 2 months so it wasn't a sudden shock to the system. I have way more sensitive sps coral in the tank that show no sign of stress either, its just this one big coral.

Gonna dip it tonight I guess. I'm also going to buy another alk test kit just in case mine isn't reading correctly.

If it's huge maybe it's no getting enough light in the bottom? Led lights seem to have that problem. T5 lights have more coverage.

When my birds eat got big it was 20"X20X15 atleast when I fragged him it died underneath as well even tho the rest was happy I just chalked it up to wasn't enough lighting getting to the bottom this was under 2 2x250 mh

What d33ps3a said!

hmmm maybe. Would this cause the tissue to go from green/pink one day to pure white from the bottom of the coral to the top of some branches in 1 day though? I was cutting off entire dead branches of the coral that were totally healthy the day before. I've never seen anything like it. I'm googling and finding people talking about Rapid Tissue N somethingorother but no one really seems to really understand whats happening. I'm reading alk, I'm reading temp, I'm reading light...lol

So ya, like everything else in reef keeping its a mystery. I'll have to test the heck out of everything tonight.

That is my experience with large SPS coral. They reach a maximum size after 3-5 years and then the lower branches no longer receive enough light and flow so they die from the bottom up. At this point I usually haul the entire coral out, break it up, start it over again from a large frag and sell off the rest.

Thanks for the comments everyone.

Could be that was just it for the lifespan of the coral.