I'm wondering if you could get powdered spirulina (I use it in my morning smoothies) and put it in the water... i use it to feed brine shrimp and mosquito larvae. Turns the water bluish green in seconds! After all, it's algae, I'm sure it'd be better than nothing...
Click here for spirulina link
That's for a 1 pound bag, which lasts ME (a human), about 4 months. A teaspoon will turn a 5 gallon bucket green.
Just a thought... Although I wouldn't even THINK about turning my beautiful tank into a green mess of free-floating particulate algae. IMO, clams are fun in theory, but will not replace a filter or make you happy.