(Back To The Forum) I run an Aquarium DNA testing company, AMA

kevgib67 · Apr 2, 2023

Welcome back Eli, glad you are here!

biophilia · Apr 2, 2023

AquaBiomics said:
We do see signatures of carbon dosing in hobbyist aquariums. A few families that we well known to respond to nutrient dosing from the literature, also are present at high levels in many tanks that carbon dose.

When we look at these tanks at the species level we often find that carbon dosing promotes the growth of specific bacteria associated with the fish gut microbiome. In other words, in a heavily carbon dosed tank the dominant bacteria are often fish poop bacteria. But those are not pathogens, they're normal members of the fish gut community even if they're not normally present at high levels in the water.

We don't generally see increased Vibrionaceae or Rhodobacteraceae in carbon dosed tanks. This may suggest we shouldnt worry too much about carbon dosing in terms of pathogens. On the other hand, we do sometimes see elevated Alteromonadaceae which is a group that includes some pathogens, and a group where standard genetic markers have limited resolution. So I can't rule it out, only say that its not the major effect we find.

In general, carbon dosing appears to heavily alter the community and for that reason I think it should probably be used more cautiously in the hobby than it currently is. It sounds like you're approaching this with the appropriate level of caution.

I especially am not a fan of hidden carbon in many aquarium products that don't list their full ingredients. Its not that I'm saying noone should add any carbon - just that the type and amounts have a very large impact on the bacterial community so my gut feeling is we should probably be as cautious about adding carbon to our tanks as we are when adding any other nutrient.

None of this is intended to say "don't carbon dose the system you mentioned" -- just my thoughts on carbon dosing in general based on what we've seen in these data.