SA grows anywhere, not just in the waterfall. I know!!! 
I have removed buckets of the stuff. At least it helps keep my water clear. I have barley straw in the Skippy and don't think it made a bit of difference. I have been using koi clay too but not systematically. So have decided to use a little algae fix and the koi clay more often. I am afraid to use the HP. One of our members who had some pretty nice fish managed to kill them all with HP.
You are correct, the SA grows everywhere; I am lucky tho that my koi love to eat it in the pond, they just can't get it in the falls/streams. This is why I use the sprayer.
I, like you, have used many many $ of barley products with zero effect, others have sung its praises, but not me!!!
Hydrogen peroxide is like many medications/water treatments that require that you know what your pond volume is and the appropriate dosage for that volume (other REALLY good examples are potassium permanganate and formalin). I have done entire system treatment of my pond with H2O2, but I know exactly how much water my pond holds. The advantage of my method with the garden sprayer is that you only use a VERY small portion of the amount needed to reach efficacy levels in the entire water column-you are only putting it where it is needed. And really, as used here, the majority of the H2O2 is consumed by oxidizing the algae and mulm that feeds it, reducing it to water and oxidized organics (harmless). This reaction is mostly accomplished prior to turning the water to the falls back on, so little if any active oxidizer reaches the fish when you turn the pumps back on.
BTW, you need to be very careful with the algaefix; I know of more people that have killed their fish with that than with H2O2 (I personally have not heard of fish kills except in aquaria with HP, but I know that there is a fatal dose level for carp, so I am sure koi and GF are succeptible as well). As I said, make sure you know the pond volume to dose properly, and I still have heard of experienced ponder that lost koi using Algaefix. Do a search over at koiphen.com on both hydrogen peroxide and algaefix and judge for yourself.
Disclaimer: HP works really well in my pond, which is 7,200 gallons with two streams, one thirty feet and the other ten feet. I use a total of one-half gallon of HP to treat both streams-this is only enough to treat 1,000 gallons if I treated the whole system. Read about HP in some of the other forums and form your own opinion!!!
Steve
