I've been fighting GDA of months and I'm tired of it. I've tried fiddling with the light levels/ferts schedule to no avail. I purchased a baby bristle-nose pleco, which did a good job controlling until it discovered it's easier to steal algae tabs from the pygmy corys and bully them around. After a few months I felt he just got too big for this tank and moved him into my 29g.
After I pulled and trimmed off all the algae covered plants I decided to throw in the town and invested in a Aquatop HOB style UV sterilizer. The sterilizer is a pretty nice unit, the UV bulb is 5 watts, included is a surface skimmer, a simple carbon and floss cartridge, a small bag of ceramic media, and has adjustable flow. I think there might just be enough room to squeeze in a 100mg bag of Purigen too. To increase dwell time in the UV chamber I turned the flow as long as it will go without getting too noisy. Not bad for $34 off of amazon.
The surface skimmer is a very nice plus. Does a decent job of removing surface scum and small floating bits of plants. Believe me if you have some type of carpeting plant you'll always have small bit of them floating around.
The downside is that it sucked in and killed one of my chili rasboras, I immediately removed it after that incident. Now i'm down to just a single chili...
I've had it on about 2 weeks and there has been a dramatic decrease in GDA! Whenever I see GDA start forming on the glass I scrap it off so that it can be sucked into the sterilizer. Hopefully in about a month I can finally be GDA free and I can remove the UV.
I lost a couple of fish due to some illness brought in from a sick scarlet badis.
1 lone chili rasbora
2 very shy danio erythromicron
7-8 Pygmy cories
1 Amano shrimp
Random fluctuating number of ramshorn snails