Well the 15 g specs are below. changes are that the clown loach is a young'in and the the betta is relocated to a private tank (recovering from recent tail injury, going to add him when the tank conditions are stable).
filter is a whisper, hangs over the back. 5-15 gallon, I can't remember the model #. It came with mesh bags to put carbon in, I have replaced that with a fluval sponge.
I inject no co2, and I will not inject it either. If my plants don't survive, I'll get new ones. Fertilizer is as far as I'll go and to get co2 going will be too big and more $ I can't spend.
Anyway that aside. I suspect the green came from a combo of changes in a very short time. I added 4 frogs, a bunch of plant - 5 stalks that are putting out new growth and roots like crazy. don't know it's name. A few days later, I added a light with better growing spectrum (18,000 K power glow). And a bit of fert (tetraplant). Somewhere in there I put in a new sponge with bio-filter media in it (it was in the filter with the old media to get bacteria-ized) and had some intake problems-not taking in very much H20 Only a trickle came out. Just a day ago, I got the intake up to normal providing good filtering and better aeration. The tank had just recovered from a mini-cycle/bacteria bloom. then turned green and fuzzy.
http://www.plantgeek.net/images/plantpics/Acrispus.jpg
In this pic, it is not the sword-leafed plant, it is the other small-leafed plant intertwined.
I have 2 small clumps of grass 2 banana plants and 1 wisteria (small), all have new growth in the 1 week since new bulb added.
Cleaning is crazy right now. Water changes every other day if it is too cloudy, every 2 or so as things stabilize, otherwise weekly. clean front glass as needed, vaccuum every 2 weeks though weekly recently, clean decorations when they get all brown, filter rinse once a month. Test water with every change or weekly when things are stable.
I feel guilty not giving any advice to civicman: Sounds like you got too many fish. You're going to have to get another tank

I smile because my aquarium hobby started with a betta in a vase and in an effort to give him a better home, I now have 2 tanks (well 3 since he is in hospital tank which was the first tank I had for him...complete circle). I swore I'd never have fish after an annoying experience as a child (we over cleaned soap and water weekly- I couldn't even keep my own room clean!). Good luck with your green.
Thanks all
Lisa