Are Bubbles Required in Waterfalls?

[dtyharry]

Don't know if anyone else has mentioned this but are bubbles technically required for this system to work or are they there just to create water flow. If the latter is the case could this not be achieved more accurately with a power head and wide outflow facing vertically upwards?
Is there not enough co2 in the water for the algae to grow anyway. It is well known that bubbles do not directly oxygenate tank water because they are not in contact with it for long enough, would this not also be the case for co2?

[kotlec]

Example.
Part of my waterfall scrubber screen is underwater. Flow is very good at this point, because of all water coming down . Guess what ? Totally bald screen down the waterline .

[Floyd R Turbo]

Bubbles create a localized turbulent flow rate at the algae mat surface. It is difficult to replicate this with a powerhead and get even flow coverage across the entire screen. This was tried a while back and submerged screens didn't work.

Also the CO2 gets sucked out pretty quick in a waterfall, then bicarbonate (alk) starts getting sucked down. This is great if you want to dose extra alk to keep pH up LOL. Providing the algae the CO2 directly as it passes by the screen and alternates from wet to dry as the bubble passes supposedly gives the algae the CO2 it needs.

[SantaMonica]

Is there not enough co2 in the water for the algae to grow anyway

No. Not when the algae are growing fast. That's why the algae start using alk.

It is well known that bubbles do not directly oxygenate tank water because they are not in contact with it for long enough, would this not also be the case for co2?

A lot of bubbles can cause the algae to be in the "air" for 50% of the time. Also, the border between the air and water, as it passes by, gives the turbulence that seems to help.

[Floyd R Turbo]

Hey wasn't this thread originally "are bubbles needed"? If so then my response was directed at a UAS setup not the waterfall setup.

[dtyharry]

I am sure I did not type in waterfalls in initial thread but there you go! I just wondered what the purpose of the bubbles was, to create circulation or provide gases.

[Garf]

Bubbles are not necessary in a waterfall but it is an improvement, in theory! Where did you hear that bubbles do not improve gaseous exchange ? Exchange of gases occur at the air water interface of which bubbles have lots. Multiply this by millions per hour and you have a massive air interface every second of every day.

[kerry]

I think he is saying that this oxygen exchange only happens at the surface of the water. There should not be any exchange in the water column.

[dtyharry]

Kerry, that's exactly what I was saying. The bubbles are not in contact with the water long enough for any meaningful gas exchange to take place. The only reason bubbles work is by disturbing the surface layer of the water. How does moving bubbles up a screen increase co2 supply to the algae?

[SantaMonica]

Because the algae are in direct contact with the air inside the bubble.