Barley put in algae infested water does help, but I have had better success with cornmeal used at 140 lbs per acre. For small back yard water features add a cupful of cornmeal and increase if needed. If the cornmeal is put in a porous bag with a rock so it will sink too the bottom of the water, the control will be more effective. Indoor tabletop water features need no more than teaspoon of cornmeal.
ALGAE CONTROL IN WATER – For floating paint-like and filamentous algae in water, use cornmeal at 5 lbs. per 1,000 square feet or 140 lbs. per surface acre. The cellulose in the cornmeal helps tie up the excess phosphorous in water, balances the water chemistry, and thus kills off the algae. The carbon in the cornmeal enables the beneficial bacteria in the water to flourish at the expense of the algae, then the decomposing algae provide a source of carbon for the bacteria. One or two treatments is usually enough to control the algae for several months. Getting the cornmeal to the bottom of the water increases the effectiveness. One technique is to put in a burlap bag with a rock. Small water features can use cornmeal in mesh bags. Pelletized cornmeal is good because it sinks. Caution: any fast algae kill from any product can cause oxygen deprivation and result in fish kill. Cornmeal from the grocery store (unless whole ground) is just the starchy endosperm of the corn kernel and not as effective.