Frustrated by him not listening? A new pond owner not listening??? Given a bunch of advice new pond owners will almost always pick the most complex, most expensive, most proven not to work, thing. Hobbies are about spending money and time doing stuff, not so much about the long term results.
New pond owners are pretty screwed. How does anyone make a correct choice with no experience? We can't of course. So I think the best filter system for a new pond owner is whatever system "sounds" best to them. Later, if he's one of the few ponders that wants to actually learn something about ponds he'll have some experience and can start the process. Or, more likely, just play around and enjoy the pond.
And as Koiguy said the bio filter doesn't have anything to do with algae. There is almost no chance this pond will even need a bio filter so it's not like picking the "wrong" bio filter would do much harm beyond a hit to the pocketbook. But again, most people find spending money fun and part of the hobby.
I will disagree with Koiguy on one point, higher plants do not remove enough nutrients to affect single cell algae much. It's an easy test. Test the nutrient level in a green pond and then again after a pond clears. The nutrient level will be higher in the clear pond. Those billions of algae died and did what...released nutrients back into the water. So why isn't there another algae bloom given all the new nutrients? There are
other things in the water that kill algae.
Algae, as pointed out, are plants. Algae take up the exact nutrients they need so they themselves would be the best plants for removing nutrients they need right? But of course this doesn't work, algae don't starve themselves. Limit growth of new algae cells yes. There's a difference.
Higher plants are at a disadvantage in the competition for nutrients. Single cell algae are floating around bumping into nutrients all the time. Rooted plant have to wait for the nutrients to come to them. And if a higher plant could remove enough nutrients to kill algae they themselves would in theory die also, wouldn't they? So the day your pond clears do all the plants die too? Of course not.
Algae blooms can grow much faster than higher plants. If a higher plant could take up and convert nutrients as fast as algae Cana would grow 8 feet a day. In a water environment algae is the 800 lb gorilla in the room, not the potted plant.
I think the reason this myth has been around forever, and will stay around forever, is a misunderstanding of how plants use nutrients. Basically most nutrients are used to build cells. And they don't need much as they get the most needed element, carbon, from carbon dioxide. They're not like us. We have to build new cells all the time to stay alive for more than a month or two. They're single cell, once built they're good to go.
Nutrients shouldn't be confused with food which is used to run the cells once created. Food of course is made by the algae using photosynthesis. Limiting nitrogen and phosphorus can reduce growth of additional algae cells. So you could get green water instead of dark green water. If you could remove
all nitrogen or phosphorus new algae couldn't grow and slowly a pond would clear as older algae died. So would all plants. But removing all nitrogen or phosphorus from a water garden is far beyond reasonable. Just dust blowing into a pond provide enough nutrients for algae. Set a bowl of distilled water outside and keep it filled with more as needed. You're likely to have algae growing shortly, although this experiment is hit and miss. Throwing hands full of fish food into a pond, fish waste, plants, bird droppings, etc...you're talking about the most nutrient rich waters on the planet.
Blocking light to kill algae is also a myth. They need very little light. A fish bowl in a living room gets almost no useable light in the spectrum plants need but will grow lots of algae. Anyone have a swimming pool covered for the winter and find the water green when the cover is removed in the spring? Covering a pond 100% with water hyacinth might kill algae. But more likely other factors brought into the pond with the water hyacinth will kill the algae first. As with Norm Meck's experiments if you add green water to a container of water from a clear pond with water hyacinth the algae will die in a few hours. It wasn't the light.
