the difference in the organic carbon source is the size of the polymer chains
Quotes from Lou @ tropic marine
The natural salt water polymer derived from seaweed is in the Reef Actif NOT the NP BACTO Balance. The NP BACTO Balance is a medium short polymer that has advantages over the monomers like vodka (alcohol), vinegar and sugars. But it is not the one from seaweed.
My understanding, as it has been explained to me by my team in Germany, is that most (not exclusively but most) of the algae and bacterial critters that we would prefer NOT to grow in our systems, have much better mechanisms for utilizing monomers than anything that is longer carbon chains. They just don't have good ability to break those longer chains down to the monomers they need. While the good guys (algae and bacteria) that are helpful to us have much better mechanisms for breaking those longer chains down to the monomers they utilize. So if you add mostly carbon chains that are more than monomers, you "target" and focus that nutrition on the beneficial critters we like to see multiply and help our closed tank system biome.
I can assure you that what he’s saying works as I have been using this product myself as a maintenance dose to my system, I find it fairly safe to use and so far I wasn’t able to overdose it, vodka, vinegar and other sources of carbon can create blooms if not used carefully.
Personally I don’t agree with this approach, I would prefer to raise my nutrients with calcium nitrate or sodium nitrate, most folks tend to use ready made products that may contain ammonia and urea for this same purpose that can be detrimental to the system as ammonia and urea can allow nuisances to bloom in out systems.
If you were to raise nutrients and add a maintenance dose of organic carbon to the system to allow beneficial bacteria to grow you would notice that in time algae starts receding, this is due to the bacteria being able to use all free ammonia before the algae. In addition most test kits including Hanna have a 0.02 error margin keeping your phosphates at 0.01 means that phosphates could actually be zero this will affect your heterotrophic beneficial bacteria that will be limited by phosphates that are fairly important for tissue building.
In the absence of a good heterotrophic bacteria population ammonia becomes more available in the system that seems to be the main trigger for nuisances in our systems, I’ve got a new thread on the research forum going we’re hopefully I will be able to demonstrate how ammonia management can be the route cause of all our problems, our tanks are constantly producing ammonia and depending how we manage it different outcomes will happen, stimulating the growth of beneficial bacteria with carbon sources seems key to redirect ammonia from nuisances to beneficial bacteria.
edit: by reducing the light photoperiod in your Refugium instead of raising no3 and po4 you will allow more ammonia to become Available in your DT as Refugium algae’s are also fairly effective at doing that , they don’t just reduce no3 and po4