My tank (link is below in my signature) was affected by spirogyra algae which is notoriously difficult to get rid of. I searched extensively for possible treatments and was never able to find a tried and true solution but I was able to get an idea of what might work. So here is exactly what I did, in painstaking detail:
First did a 50% water change. I uprooted all the plants, with the exception of my glosso. Separated them all into bunches by species, then put them in a number of 5 gallon buckets, with only 2 or 3 species in each bucket. I filled each bucket maybe a quarter of the way with regular tap water at around room temperature.
I used 2 different dish washing tubs: one for the H2O2 bath and one for rinsing. In the red tub, I put 1 gallon of room temp tap water and 8mL 3% H202. In the black tub, I put a little over a gallon of room temp tap water.
I took each plant, 1 species at a time, and rinsed thoroughly at the faucet. As I rinsed, I held each individual stem, suspended upside down, and tried to remove any green threads that I saw. Also, as I ran them under the water, I would place them in the palm of my hand and run the stems across my hand, passing them through the stream of water. As I did this, more green threads would come off. I threw out any severely affected stems, only keeping healthier, neater, and less affected stems.
I placed each plant, 1 or 2 species at a time, into the H2O2 bath and set a timer of 20 minutes. While one group would soak, I would be rinsing and cleaning the next bunch to be soaked. Once the time was up, I put on latex gloves to avoid prolonged contact with H2O2. I rinsed the now-treated plants as I did in Step 3, again looking for and removing any green threads and removing at leaves affected by BBA. After rinsing, I placed each bunch into the black (plain tap water) wash tub and let them soak there for 10-20 minutes before I removed them from that tub and floated them in a 10 gallon aquarium filled ~5 gallons of regular tap water. Throughout this process, none of the water was de-chlorinated. I eventually got all of the plants treated and rinsed and they all were floated overnight in the 10 gallon aquarium, mainly because I did not have time to replant on the same day.
Side note: I divided and thinned out the blyxa japonica quite a bit, removing several lower leaves and throwing out severely algae infested bunches. I ended up with ~15 smaller, much thinner bunches that appeared to be algae-free
Side note #2: I changed the water in both the red (H2O2) and black (tap water) tubs after every other batch soaked (roughly every 4 species treated)Step 5:
I removed the driftwood, rinsing well in tap water and scrubbing with a fresh sponge and a toothbrush to remove any clumps of BBA that I had killed with spot treatment. I removed all the moss from 2 of the pieces of driftwood that I had tied moss to only a few weeks ago. On a third piece of driftwood which had quite an accumulation of algae-infested fissidens, I took a pair of sharp scissors and carefulled cut away the infested moss just above the surface of the wood, leaving only short stubs what had attached to the driftwood. I then rinsed it thoroughly, them dipped this piece in the red tub, but this time containing 1.5 gallons of tap water and 16mL of H2O2 (extra strength solution, bringing out the big guns). I soaked this piece for 15-20 minutes, then rinsed it thoroughly for several minutes. I then placed the driftwood back into the tank.
I scraped algae on all the glass surfaces of the aquarium, let the filter run for an hour or two, light and CO2 off, then did a 50% water change, lightly vacuuming the substrate throughout the tank. I ran the filter for another couple hours, with the light and CO2 off. I leveled all the substrate to the general desired shape. I then turned off the filter, waited about 5 minutes, then spot treated my glosso using a total of 20mL 3% H2O2. I let this sit with no water flow for around 15 minutes, then ran the filter again for the afternoon.
replanted all the plants, keeping only the healthier-looking stems. It looks pretty thin right now, but everything will grow back with time. I have re-dosed the aquarium with macros, but much lighter dosing both to limit accumulation of nutrients for the time being and due to the greatly decreased plant biomass.
I plan to clean the filter and rinse well with de-chlorinated water soon as the final step (this is the third day after beginning the treatment). As of right now, I do not see any green threads of algae on any of the plants or attached to any of the driftwood. Hopefully this extensive, labor intensive, and time consuming treatment has worked. I will reply back to this thread later on as I am better able to tell whether this treatment was successful or not. I hope this might help anyone else who might have a similar problem.