Dear Awaking Froggie,
The microbial life in a pond accounts for over 98 % of the life in a pond. This is a huge dynamic where many variables are present. In the Middle Ages, pond keepers in Scotland noticed if barley straw was placed in the castle moat, algae was retarded. I have been asked many times how this works and have determined there are several reasons.
To use barley straw, you must have an aerobic fermentation of the straw. This means you cannot use packed bales. The barley is loosely packed in biodegradable onion or hemp bags so air is all around the straw. The straw is allowed to ferment partially submerged at the shore edge (1/3 in and 2/3 out). Place about 10 yards apart. Barley straw is known to be a sweet straw (horses love it). The sugars in the straw when fermented in the air turn into vinegars. This lowers the pH making membranes impermeable not allowing membrane fusion needed to have sexual reproduction. No sex: no algae. But this is only partially what is happening.
Fermenting straw leads to a diverse microbial population where a food chain is established with the bacteria fermenting the straw feeding larger invertebrates; and all of the way up the chain to insect larvae. Many of these larger life forms eat algae. And in turn are eaten by frogs and fishes (and the turtle in the pic). When the number of algae predators is balanced with the amount of algae, the system is balanced and no excess alga is present. Barley is also known to have biocidal activity. This means a compound in the straw kills algae. I believe this is partially true. More likely, the fermentation encourages common soil bacteria to produce toxins that kill algae.
The ultimate dynamic involved is the amount of nutrients in the pond. The higher the nutrient load, the larger the algae bloom. If nutrients are too high, barley won’t work. However, if you use barley in concert with bottom diffused air and pond bacteria, you reduce the nutrient load and encourage algae predators leading to reduced algae load.
Using barley is a Band-Aid™. The natural way is to ferment a log; you get the same effect (see pic). You pick a log that doesn’t have pitch or tannins: maple, alder, willow, cherry, apple (deciduous). Conifers and others evolved tannins (chloro-phenols) that are liver toxins for insects. (Why bark dust kills ponds.) We wish to have invertebrates. To establish the rot, you can split open the log and put soil in the cracks and plant with seeds (flowers). This allows a fungal rot to start that allows them to degrade the cellulose sugars in the log that many life forms can use. I have noticed that once the rot is established, a pond becomes healthy. Take care of your bugs!
Planting shore plants is the ultimate solution to algae problems. Using slough sedge, willows and cottonwoods, allows the pond to respire correctly and bacteria living on river gravel compost nutrients in the pond. This leads to diverse populations of microbes that are the basis of life in the pond ultimately feeding your fish and you froggie.
Froggie, the bugs rule! Gluggy, you cannot solve your algae problems just with barley without addressing the entire ecosystem most importantly the microbial life. No more than you can address a fishery loading streams with fish. You will be awakening soon; I hope we do too.
Affectionately yours,
PonDoc from the pond