is the co2 on a bad controller? All that bba still makes me think co2 is either irregular or not enough.
Either that or you still have a lot of cleaning to do (organic build up)
As you said, algae is most prominent on unhappy plant parts. Dirty conditions aside, algae is present because the plants arent happy. Whether it be too much light or poor co2 or a fert imbalance.
GSA is no different. High P levels might kill or suppress it, but "low P" isnt the root cause. The root cause is just like every other algae, unhappy plants/dirty conditions.
Do a big water change and aggressive cleaning. Clean the filter. Pinch off ALL dead or dying leaves, any leaves with BBA. Replant the nice stuff.
Light vacuum the substrate surface, get all the bba you can out of there. Scrape the glass. Take the drop checker and powerhead out and spray them down with peroxide to kill all that algae, then scrub em down good.
Then, cut P down to around 3 ppm per week. Dont worry if a little gsa pops up the first few days or week or two. This is normal while things adjust to the new levels. Just scrape it off and be patient.
Stay on top of the cleaning, plant pruning and maintenance.
Honestly I feel like I may need to just replace the substrate completely at this point.
Even my best vacuuming creates so much more goop in the water column
At the rate certain plants get BBA I'd have to cut them down to half an inch or so.
But I guess I need to get to the root cause of the plants being unhappy.
I've had this issue (GSA like mad, BBA) with the following lights
1 Current Sat + pro
2 Current Sat + pro
1 Kessil A160We
Quad t5 HO
No significant difference in growth rates of either algae
I've ran Inline diffusers, in tank diffusers, reactors til my fish are doing headstands in the substrate
I've tried nearly everything under the sun I feel like, and while I'm seeing some improvements I've been at this for over a year
And I still cant freaking grow rotala rotundifolia lmao.
edit: Co2 isn't on a controller, its on an ISTA reactor, now coming on 3 hours before lights and off half an hour before lights