Coraline algae not growing

[Arnaldo24]

hi guys
finally i decided to start a thread looking for help/advice on what to do since im very close to breakdown
been reefing for 15 years or so but never face this problem

a while back my coraline algae started to die/flake off and my rock started to turn dark/black every zoa i had on rocks die, every encrusted monti die i even lost a few fish

i did battle some torch eating flatworms and i actually lost the battle lost all my torches and i had a lot. lost lots of hammer colonies and i was close to just throw the towel

prior to that i was a no water change reefer and evertything was growing great and looking awesome but since the problem started i started doing large water changes my system is 400+ gallons so meaningful water chnages are not ideal sometimes but i did them

i didnt add anything to the tank for close to a year trying to just let it run. i added a few sps frags and some zoas with no luck

the rarest part of it all is i stop and sold my calcium reactor around 6 months ago and my alk was steady at 8.5 till last week when it finally dropped to 8.0. i do have still fair amount of corals that should make my alk drop but it didnt.

i send an ipt test and i will post the results, nothing major, i dont mess around changing things or trying new things and i have a bit of experience reefing but i just figure this out to the point that im loosing interest but i have my fishes for years some over 6 years and i really would like to keep them

heres a run down on my system and i will add some before and recent pictures and or video.
any hint on where to look or what to change would be appreciate it.

360 gl miracle aquarums display
100 custom sump
SRO6000 skimmer
full apex controller
7 stage 150gpd rodi
6 gen6 radions blue xr30

 

[reefpanda]

Sorry for having to go through this. Could it be due to old tank syndrome?

 

[Arnaldo24]

Not sure. I set it up during covid. So its not that old

Here some pictures of how it looked before and how empty looks now

 

[Arnaldo24]

Here how it looks recently
Not 100% complaining tho since all this happing my mushrooms are growing insanely fast.
Godzillas and King Kongs dropping babies weekly if no daily.

 

[reefpanda]

Great looking tank! Can you test for nitrates and phosphates?

 

[Arnaldo24]

Tst was done 3/29/25
Since then i started using gfo again and water changs to lower my phos. Will post later todays tst result

 

[reefpanda]

You got this and start bringing the phosphates down but slowly, with what you’re doing. Don’t want to shock the remaining corals. Let’s wait fir others to chime in

 

[Arnaldo24]

I started with gfo half of recommended
And also 30gl weekly water changs
Remaining corals seem to be fine. Everything stop dying. Few hammers i got are doing great. Mushrooms are growing crazy and i have 1 remaining head of torch thats also fine
Dying corals stop about 6 months ago.
But how is it possible my Alk didnt move from 8.5 for months.