Mrs. Fishbone,
I am not an expert in the field of lighting, but I myself have also been doing a lot of studying and heres what I can tell you.
Your lighting is pretty much pathetic if you are using Co2. With the added Co2 in the system your plants are starving for more and better, but look out, with the more light your slow growing plants will grow like weeds in the right conditions. Co2 is actually an overkill with your plants but thats ok, growing them will be easier.
Look for a light that is T8 (type of bulb) and something that is possibly brighter (Watts). I know you are probably limited by your lighting hood, but I put in way brighter lights in my hood than I am supposed to and it just takes longer for them to get going in the morning. You have plants and fish, so also look for a light that is Tri-Phosphor or Full-Spectrum. Basically anything is better than the bulb you have in there now. Any pet store should have what you need and the employees should be able to help you choose which kind.
For the algae growth try several things... One, put your light on a timer, have them turn on for 5 hours then off two (mid-day) then on five again. I read a lot about this and its said to confuse algae to death, but your plants don't seem to notice a thing. Two, you say your adding plant fertilizer, I have always had huge algae blooms if I go by the directions on the bottles, ESPECIALLY IF YOU ARE USING Co2. Try cutting your dosage in half or more and see if your plants even notice, the algae sure will. Three, make sure your tank gets NO SUNLIGHT or it doesn't matter what you do short of a UV Sterilizer your algae will just keep growing. Finally Four, if your Co2 is fluctuating a lot, such as going from 15mg/l to 30mg/l every day then your algae is taking advantage of this, make sure the levels in the tank stay equalized and steady.
Also, every time I get brown algae it is because of Ammonia or Nitrates or Nitrites... Make sure thats not it.
As for your substrate the one I hear about the most hands down for plants is Laterite. If you want a sand on top then make sure you place a net or some sort of mesh to keep the layers separate from each other or you will get an ugly mess down the road with your substrates. If you want black sand then Tahiti Moon Sand, black Pool Filter Sand or Black Play-sand is what you will want (the later two kinds are at your local hardware store, make sure you rinse them good). If you do sand you have to take into account that sand will compact and crush your plants and will also form toxic gasses if to thick. Most people to fix this will just get Malayan Live-bearing Snails (MLS) which will swim all around in your sand keeping it from compacting and from causing gas problems. You should still also sift through the sand with your fingers or something each time you do water changes. If you want to go more in depth with sand info there are a million threads on the subject. This one is a good one to get you started:
http
/www.fishforums.net/index.php?showtopic=71597
Good Luck!
