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.

[kerry]

I can see the algae pulling out the co2 as bubbles goes across it but no exchange happens in the water column itself.
Has anyone noticed less bicarbonate being used in their tanks while using the UAS? My 40G water fall works so well I am afraid to pull it off and make it an UAS if the dosing of Kalk is going to be no different.

[Garf]

So I could bubble loads of Co2 through my waterfall, blow the surface of my sump with fresh air, and my ph wouldn't change? Well it can't change if there is no uptake in the water column.

[SantaMonica]

CO2 would lower your pH very quickly.

[Garf]

Yeah, it doesn't seem possible NOT to change the composition to me. I am now in a position to test this and will post results. I will definitely be disconnecting my sump from the display first though.

[WAK]

Some co2 will dissolve in the water and create carbonic acid. Lowering the ph

[Garf]

Some co2 will dissolve in the water and create carbonic acid. Lowering the ph

Just been reading some stuff on micro algal cultures and it is possible to reduce ph to 5.5 using co2. Considering that the air in houses contains 2 or 3 times natural co2 levels, I would consider that this is already co2 enriched and doesn't need supplementing any further. The ph on my screen is not increasing during the light phase, suggesting that co2 is being utilised by photosynthesis, supplied from the air bubbles.

[WAK]

How are you getting the air to the screen , is their a lot of improvment in growth with air supplied.

[Garf]

How are you getting the air to the screen , is their a lot of improvment in growth with air supplied.

WAK - just a simple air line into the ATS feed pump impeller. As to any improvement in growth it is too early to tell. I am pretty much in the learning phase of this scrubber stuff. I started this bubble screen idea with the outlook that "well it can't do any harm". My motivation arose to reduce the alkalinity consumption which comes about when co2 is low, and algaes are growing fast. For me, any improvement in algae growth would just be the icing on the cake.

[herring_fish]

What you are trying to do with the bubbles, is to break down the boundary layer by providing very localized random turbulence.

I copied this in part, from another article, "There is a microscopic layer of water that touches the surface [of each strand of algae]. The friction created by the liquid passing over the solid surface causes the water to slow down. The thickness of this layer is less than 1mm, above this friction is lost and water passes freely[ without exchange], so if water has a velocity of say 30cm per second the layer of water over the surface could be less than 3 cm per second."

As you know, algae has a very high metabolism and it needs to be able to exchange CO2 and other materials at a high rate. Swift water motion over all sides of the strand is essential. If two strands are stuck together, there respiration is cut almost in half. If five strands inclose one, the outside strands fall to less than half each and the one in the center can die from asphyxiation so to speak.

I did read back up on the bubbling and there is some exchange directly with the air in the bubbles but not a lot. CO2 injection also does help but again, not a whole lot. Commercial guys use it if it is free but the increased production won't pay for itself. The much more important factors are good water contact with the entire surface area of each strand of algae and the speed at witch that happens.

Bubbles help promote turbulence and turbulence breaks down the boundary layer for better, faster contact with the water.

[Garf]

Sounds good to me.

[Garf]

A bit of an old topic I know, but I thought I would put this one to bed. Have recently added a DIY Co2 generator to my waterfall feed pump intake. PH has reduced, indicating Co2 is being taken into the water column.

[crashmushroom]

I copied garf with the air injection (not co2) to waterfall and my system stopped drinking alk, im not brave enough to try co2 :-)