Most coral receding with no explanation .

[Stormhaven]

Hi guys so I'm posting for a friend.
His tank has been experiencing mass coral recession for three weeks .
What we have done to try and fix it .
Removed leather corals .
ICP test
Replaced vectra m2 as it had a odd smell like burnt rubber pump still functioned and I'm not sure where the smell was being generated .
Replaced heater just incase it was leaking stray voltage.
And still nothing
ICP test showed low potassium and iodide.
He carbon dosers using Nitra guard
No3 <10 Salifert
Po4 recent test <20 Hannna

No lighting changes and pumps were all taken apart and expected for rust .
Any ideas ?

Thanks.

 

[blaxsun]

Which Hanna tester are you using?