I've seen it. Yes, antibiotics do nothing.
If you look at CO2, some good temporary mechanical filtration, clean and preen the algae off as best you can, but it looks to be more a CO2 issue.
I've had 3 tanks with it in the past.
Your Eustralis(P. stellata) looks like it's hurting for CO2, stunted tips etc.
Blyxa especially is telling.
It's a very fast growing weed.
I only had this when the CO2 was poor, and all the 1/2 dead, slowly dying plants, loss leaves floating around etc, accumulation of organic plant waste helped the alga.
Once the CO2 was addressed, the issue has never returned.
One tank has a pair of CO2 reactors, the gas tank ran out and folks messed with the flow rate. Another, the filter would clog in 1-2 weeks and it was tied to the CO2 mazzei valve which had lower pressure, thus less CO2 flow coming into it.
Another tank had progressively more and more Plant biomass and did well until it was fully planted. Then trimming it really never helped that much, I had to add more CO2/flow.
Eventually, I reduced lighting for two of these tanks and switched out the CO2 method and kept a more careful eye on it.
Not algae issues.
No loss Blyxa leaves etc.
Blyxa is a good case study for CO2 because it grows so well when you have good ample CO2. Otherwise it does rather poorly. Loses leaves, slowly gets smaller etc, covered with algae etc.
I have Bylxa is several tanks and this algae could easily move from one tank to the other, I took plants from each tank and moved them around without issues or a new infestation............the sediments where the same as was the dosing.
So light was different, but not that much nor has light really every been much factor unless it's simple too much, too long etc, PAR measurements are all fine.
So not much is left other than CO2.
In 2 of the tanks, simple adjustment of CO2 "cured" the issue.
One tank is a client's and they abuse it.
So it's harder to deal with.
They now add Excel, but they do not add it consistently nor the ferts.
I might have to put a lock on the CO2
This and BGA both appear related to the losses of organic matter from plants, decaying plant leaves etc.
What is your suggestion, blackout and increase co2 levels? Or just increase co2 this time? Right now i have PH 6.4 / KH 2 (measured at 23ppm CO2). I am running a biofilter, not as i had, but now only with white filter and blue filter material (those matts). I ordered an Eheim 2080 to assist in filtration. Could it be a N disturbance and if so, how can i fix it?