Here is an update about this issue, and unfortunately not that good. My situation with algae got worse despite all my efforts to combat it. Here is the entire story to make it clear once for all:
1. Once I setup my tank 5 years ago, I could enjoy an algae free environment for years until about 1 year ago when I began seeing some GDA on my glass. I didn't care much until a few months ago when it got worse and GDA appeared on the glass just after a few hours of scraping it off. Also, most of my Rotala Nanjenshan began to struggle growing because the same GDA (or similar algae), began growing on it, prevent the plant to grow and thrive well.
2. I tried any sort of change and experiment: increasing light and corresponding fertilization, Co2, etc... decreasing of light, and decreasing of fertilization, Co2, etc... blackouts, light "siestas", changed light, different light color temperatures, etc... I tried everything. I also tried to increase Co2 without increasing dosing: no luck. I also increased internal circulation a lot by adding an additional pump and making water circulate in any direction: no change after 2 months doing that. Didn't matter!
3. So, desperate a couple of months ago, I tried the suggested method of "let GDA grow" for 4 weeks... and it seemed to work for about 7 days, then it grew back. Yes, despite it was better, this damn GDA was back again. So I thought: maybe is my dosing regimen to lack some nutrient... so I increased it, and with the fact I am using the Seachem product line, I tried to follow the schedule they suggest:
http://www.seachem.com/support/PlantDoseChart.pdf
thinking "Even if it looks a lot of fertilization, I can always solve the problem with weekly water changes", sort of the "water change -> reset" concept the EI technique requires to work.
5. Result? Everything got worse: after just a few days, I began to see a sort of "green fur" algae bloom on my Sword leaves as well on some of my Ambulias which have always been very strong and algae free. So after one week of increased dosing, I got back to regular dosing, but as today, after 3 weeks, the situation is even worse: GDA is back as it used to be 2 months ago (it appears after a few hours of scraping it off the glass) and the "green fur" algae spread on almost all of my Ambulias making them grow less.
I am almost desperate because looks like the situation is out of control. And I have no idea what do try else. Also, there is a big problem now: I am going to leave for vacation in 7 days and I will be gone for 1 month. What to do during that time? I will be unable to both dosing and change water.... and I am afraid to find an even more worse situation when I will be back... I was thinking to reduce light to reduce the need of dosing, but I am not sure if it is the right approach. What is confusing is that most plants grow well, very well, despite the algae issue, so I don't think there is any big issue with water quality or similar.
To let you better understand my situation, here is my tank and contents configuration:
1. Tank size: 75gl
2. Filter: wet/dry sump with Eheim Compact+ 2000 528gph
3. Pressurized Co2 system with Aquamedic 1000 inline reactor
4. Light: 140W fluorescent tube lights 6500K
5. Substrate: Ecocomplete
6. PH 6.4-6.5 (let me know if you need more measurements, I don't measure that often)
7. Weekly 50% tap water change.
And here are my plants:
1. 3 Swords (growing great)
2. A lot of Microswords (growing great)
3. Several Alternanthera Reineckii (growing great)
4. Several Vallisneria Americana (growing great)
5. A lot of Anubias (growing great)
6. A lot of Ceratophyllum demersum that I use as "fast growing plant" (growing great)
7. Java moss (used to grow better, not it is pretty dirty and often get covered by some algae)
8. Rotala Nanjenshan (used to grow great, now struggling and covered by some sort of GDA algae or similar)
The worst plant is definitively Rotala Nanjenshan.
Also, besides not too many fish, I have a nice anti-algae crew such as about 10 Otocinclus, about 20 Amano shrimps and dozens of Red Cherry shrimps, but looks like that's not enough (they cannot eat GDA and they don't look much interested in the "green fur" I wrote about above).
Well, if you have any idea, tip, advice or simply different thoughts, I am eager to hear from all of you guys.
Thank you so much and talk you soon!
All the best,
Fab.
PS: Here is a picture of my tank taken right after the "let it grow" strategy:
http://www.virtualsheetmusic.com/storage/tank.jpg