Is this a diseases or just malnutrition

No its not the fish please take a look at the plants and the black spots on them, it seems to only be on this particular plant and start from the bottom and work its way to the top of the plant leaving just the stork and some roots.

 

@jpvd007 - Couple of Q's mate.... What ferts do you use (Especially - what is your Carbon source)? I see Discus in there...what Temp does this run at? Think the reason for the leaf degeneration is a combo of these two answers...

 

Hi @azurekoi

My carbon source is threw excel and the tank temp is at 28. I did cut down on frets (flourish) as I was treating for white spot (and I don't like to much additive at once in my tanks) with a product of Henks I can't remember what it's called but it was a 10 day fix and smelt like mint, that was about weeks back that I stopped the dosing the a weeks rest and a water change and then a dose of Microb-lift special blend and I have my suspicions? I started the excel again last night so there is carbon in again after say a 5 week break. Much to my utter frustration the black beard algae is back due to the lack of carbon.

 

1st off 28 is at the top of that particular Hygrophila's accepted range... 30 degrees and it starts struggling... so no carbon for 10 days ish... Hmmn - seems plant went into "Survival mode" - the plant decided to make lots of babies at the plant nodes and withdrew all it's energy from the mature leaves to push into developing the babies...
Dont fret over it - with now resuming your ferts/Excell,all those little babies will soon be healthy plants...