I tried asking about this on other forums but couldn't really seem to find anyone who really knows what's going on. I don't just want to know what to do, I want to know why, I'm sure someone here has a good understanding of the chemistry and biology involved which is what I really want to understand.
I have a 10g and initially had Hygrophia polysperma and a java fern planted in it. Over the course of several months the blue green algae (I'm assuming that's what it is based on descriptions, it was like a thick black sheet if it grew long enough) totally took over my tank. It didn't seem to matter how often I would clean it out, or even if I would physically remove it from every single leaf of my plants, it would come back with a vengeance before my next water change (and I would do them weekly). I had two screw-in florescent bulbs, 9w, and then tried 13w, and that only served to increase the algae's spread. I tried major water changes, even at one point totally removing almost all the water and replacing it. This only resulted in adding a brown algae bloom to my issues. I tried diy co2 which helped the plants increase their growth but didn't slack on the algae at all. Finally when all of my plants were dead except one part of the java fern and one tiny polysperma plant, I removed the florescent lights and put two 15w incandescent lights in since I thought the battle was lost. Then to my surprise, the java fern started to really take off. It doubled in size in a few months. The polysperma also started growing, and even though the leaves weren't the verdant green that they were before, at least it wasn't dying anymore. Another tiny polysperma plant that I figured was too small to take root, also started growing.
So then I thought - great, my algae problem is finally over! I switched back to florescent lighting, starting off at only 6 hours a day to see what would happen. Within days the algae was back again but not with quite the same vengeance. I scrubbed and scrubbed and fought it this time but again it seemed like a losing battle. Then, I came across a study that said that high phosphate to nitrate ratio can cause issues with bga. So I got a phosphate remover and added it to my filter. Now it seems that I finally have everything under control and I can even have my light on for 8-10 hours a day (yes one light, I'm still afraid to use both).
So what I want to know is this: Is phosphate present in tap water? What else could cause bga issues of this magnitude? Also, how can you tell the difference between regular green algae and bga? I have some algae on the glass now and it's not growing fast, I would like to know what it is. Another question I have is, has anyone done co2 using paintball cylinders and if so how did you hook it up? I totally LOVE aquatic plants in fact even more than fish sometimes. My dream is to have a 90g filled with all kinds of plants. (I think I have fish because I don't want to look stupid having just a tank full of plants. No offense though.)
Just as a sidenote, my tap water here is about 6.6 pH out of the tap, NO KH or GH at all. I use a few small seashells to add buffer to the tank water. Also the tap water here has a yellowish brown tinge on it. Since there's no GH I'm thinking tannins maybe? Or could it be some mineral?