Does running carbon hurt plant growth in reef tanks?

[mndfreeze]

Title basically says it all.

Trying to figure out why suddenly I can't keep macros alive in my little hang on back finnex breeder. Chaeto used to grow like a weed in there. The only things I've changed that I can think of is I added mud from florida pets to one side of it and some burrowing brittle stars. It seems to grow cyano a lot on it. Not sure if it can outcompete macros or what.

The other thing is I threw a bag of activated carbon behind my overflow spill over. This is an aquapod 24G cube, its old, the back chamber design is garbage. Flow goes like this through my tank system.

Distplay right side overflow into back chamber. Back chamber is one big chamber with a cut out at the bottom connecting the two, but has a divider up the middle. Right behind where the water flows into the back I have my skimmer, and aqua C remora. Bag of carbon sits there as well.

Left side "chamber" has my return pump at the very bottom, and a small pump and tubing that goes up into the finnex 1G HOB breeder box setup as fuge.

I've said this already before so before anyone says "it isn't big enough for nutrient export" etc, the goal is just a little fuge for pods and other weird microlife.

So does carbon strip away vital stuff for macro algae? Or is the cyano mats growing on the few inches square of reef mud out competing? Looking for any ideas.

 

[Michael Hoaster]

Activated carbon does compete with plants for dissolved organic carbon (DOC), so I only run it when I'm trying to get rid of something. I doubt it is THE problem though. Cyano bacteria also competes with macros for nutrients. Macros need MORE nutrients than micros. The biological (bacterial) filter also competes with macros for nutrients. If your tank has recently matured, bacteria, combined with these other competitors may be limiting the nutrients your macros need. Assuming adequate lighting, it seems likely you don't have adequate nutrients to grow macros.

 

[Subsea]

DOC is produced as leakage from photosynthesis. Not all DOC is the same and not all activated carbon is the same. Coral DOC is full of lipids & protein and macro DOC is full of carbohydrates. IMO, it is always good to use modest amounts of activated carbon changed out every two weeks.