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?