The thing about a waterfall is that is relies on the temp of the water to a degree, since it cannot create bubbles that rise up under each plant. To elaborate, the amount of o2 water can hold is inversely related to temp, so you can easily reach a solution temp that will not hold enough oxygen across the entire size of the dwc container.
I'm sorry, but I disagree with most of that..
Temp and DO are not directly related to water falls or any other type of aeration. The temp is what ever it is independent of aeration type. True that cold water holds more oxygen, but so what? if you dont aerate cold water the DO % will be lower then if you DO aerate it. The same applies to warm water.
No type of aeration is dependent on temperature to work or not work. They all work on cold or warm or hot water equally well.
Secondly, you will never have different amounts of DO across any body of water unless it is stagnant. As long as it is mixing - from a pump, or bubbles or a water fall or flumming - the DO will be the same in every part of the bucket or system. Thats a result of that slow rate of solution of oxygen into water. Its the reason we do active aeration in its various forms.
You can bypass this by releasing bubbles directly under each root zone.
No. If anything bubbling increases water temps because the pump is putting warm air into the water. And again - every part of the bucket will have the same DO unless the water is stagnant - which it wont be if there is bubbling or flumming or a water fall.
Another thing to consider is (other than cost) why would you want a water fall creating aeration over something like this? (I am in no way affiliated with this product or company selling it, just using it an as example)
One advantage of a water fall is it can be driven by the same pumps that already in use in an RDWC system. Plus, water falls put LESS heat into the water than air pumps.
As far as noise, the larger the pipe size for any given water flow rate, the lower the noise. You dont even really need it to "fall" very far. You can also try your idea of the manifold. Just have the outlet T off into a manifold and have several outlets. Each one will have only a part of the total flow, so will make less noise.
Again - aeration works by increasing the surface area of the water that is exposed to the air. All you need to do is have the surface of the rez refreshed as quickly as possible. Faster makes for more noise, but you really dont need to go over board.
If the water fall turns out to be too noisy for your living room, change over to fluming. It is just as effective. To flume, just have the pump outlet at the bottom of the rez pointing UP so the pump output roils the surface of the rez. You can actually just sit the pump in the bottom of the rez and point the outlet at the surface. if you do that, I would think the smaller pump would be fine. Or you can just use the return pump you already have in your system.
You do need to be sure you rez has fresh air available and is not 100% sealed. It doesnt need to be wide open either. Oxygen diffuses through air really fast - especially compared to water.
