Does an Algae Scrubber reduce Dissolved Organic Carbon through Photosynthesis??

[Scrubber_steve]

Air exchange is a key variable in a reef. Here, we identified another driver in carbon to feed algae.

In regards to CO2, the aeration of water by skimming is normally for removing excess co2, from the fishies, etc. In your example of the concrete tank above the limewater created ate up the co2 to a great level.

My scrubber does more than enough air exchanging. And I'm happy with an alkalinity level at 125ppm.

 

[Subsea]

Carbon Dosing Nature's Way

Carbon Dosing Nature's Way

I run an algae scrubber. Besides live rock, activated carbon & a 30% water change every month or two I have no other filtration.
I have several Tangs & various corals. PO4 & NO3 read zero.

A noticeable difference in my tanks water chemistry occurred after the scrubber screen matured. The alkalinity fell but settled at NSW level; 125 ppm. I add bicarb, it settles back at 125ppm after a couple of days.

This is fine.

The reason my alkalinity stays at a lower concentration is due to the action of photosynthesis by the algae in particular. Why!
Sea water, at a typical pH of 8.2, contains virtually no co2. (see Photosynthesis and the Reef Aquarium, Part I: Carbon Sources. http://reefkeeping.com/issues/2006-10/rhf/index.php )

So, Algae, & all other photosynthesising organisms, need to derive their source of carbon during photosynthesis from other sources using various mechanisms. Bicarbonates in the water is at least one source. This is why my alkalinity content falls.

So, what I am wondering is, why my algae continues to grow strongly but the alkalinity level remains at 125 ppm? Why doesn’t the alkalinity continue to fall as the algae continues to grow & continues to need a source of carbon?

Is the algae able to derive carbon from the dissolved organic carbon (DOCs) in the aquarium water?

Not quite. As algae use bicarbonate & carbonate from the water, it consumes the dissolved co2 gas in solution. This in turn due to “partial pressure law” allows more atmospheric co2 to enter the water.

You are carbon dosing, nature’s way.

 

[Scrubber_steve]

Not quite. As algae use bicarbonate & carbonate from the water, it consumes the dissolved co2 gas in solution. This in turn due to “partial pressure law” allows more atmospheric co2 to enter the water.

You are carbon dosing, nature’s way.

Yes; I've since learnt from the guru Farley that the alkalinity doesn't fall because the hydroxides that remain after the carbon atom is removed via photosynthesis instantly take up another carbon atom. Its like when using kalkwasser (calcium hydroxide); the hydroxide is what raises the alkalinity.:rollface:

 

[Belgian Anthias]

I run an algae scrubber. Besides live rock, activated carbon & a 30% water change every month or two I have no other filtration.
I have several Tangs & various corals. PO4 & NO3 read zero.

A noticeable difference in my tanks water chemistry occurred after the scrubber screen matured. The alkalinity fell but settled at NSW level; 125 ppm. I add bicarb, it settles back at 125ppm after a couple of days.

This is fine.

The reason my alkalinity stays at a lower concentration is due to the action of photosynthesis by the algae in particular. Why!
Sea water, at a typical pH of 8.2, contains virtually no co2. (see Photosynthesis and the Reef Aquarium, Part I: Carbon Sources. http://reefkeeping.com/issues/2006-10/rhf/index.php )





So, Algae, & all other photosynthesising organisms, need to derive their source of carbon during photosynthesis from other sources using various mechanisms. Bicarbonates in the water is at least one source. This is why my alkalinity content falls.

So, what I am wondering is, why my algae continues to grow strongly but the alkalinity level remains at 125 ppm? Why doesn’t the alkalinity continue to fall as the algae continues to grow & continues to need a source of carbon?

Is the algae able to derive carbon from the dissolved organic carbon (DOCs) in the aquarium water?

The effect on alkalinity depends of the nitrogen source used

ammonium as nitrogen source

16NH4+ + 92 CO2 + HPO42- + 92 H2O + 14 HCO3-→ C106H263O110N16P + 106 O2 EblingEnCo2006)

nitrate as nitrogen source

16 NO3- + 124 CO2 + HPO42- + 140 H2O → C106H263O110N16P + 138 O2 + 18 HCO3- EblingEnCo2006)

http://www.baharini.eu/baharini/dok...monium_reductie#heterotrofe_ammonium_reductie

 

[Maivortex]

No, only heterotrophs or mixotrophs can.

There are numerous species of algae that are heterotrophic and mixotrophic..

 

[Belgian Anthias]

The effect on alkalinity depends of the nitrogen source used

ammonium as nitrogen source

16NH4+ + 92 CO2 + HPO42- + 92 H2O + 14 HCO3-→ C106H263O110N16P + 106 O2 EblingEnCo2006)

nitrate as nitrogen source

16 NO3- + 124 CO2 + HPO42- + 140 H2O → C106H263O110N16P + 138 O2 + 18 HCO3- EblingEnCo2006)

http://www.baharini.eu/baharini/dok...monium_reductie#heterotrofe_ammonium_reductie

Given a choice, ammonia is preferentially taken up by algae and algal phytoplankton over nitrate.
This is for the biosynthesis of saltwater algae. Respiration is just the opposite of the above equations. EblingEnCo2006) http://www.baharini.eu/baharini/doku.php?id=nl:makazi:het_water:ammonium_reductie

 

[NS Mike D]

Organic Chemistry and the need to sleep (7am 5 days a week) is what stood between me and my Pharmacy degree (ended up taking a much easier path and earned a degree in economics ;-) )

Now 4 decades later I find myself reading this thread over and over with, might I admit, a bit of enthusiasm and interest.

Sometimes, life's sense of humor can be bitterly ironic.


I'm enjoying these threads that explore the bio-cycles going on in our tanks , and not just "I have algae, which over-priced snake oil do I need to add to my tank so it magically disappears in a week?"