Are Bubbles Required in Waterfalls?

[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.