Are "rocks" really nutrient sinks?

[Hermie]

I'm skeptical that reef rocks (dry rock namely) actually bind up and release substantial enough "nutrients" to fuel nuisance algaes. Anecdotally, I hear how new "dry rocks" will release their phosphates/nitrates/etc and cause algae, but is this really the case? The theory being that if "dry rocks" are allowed to leech their "nutrients" then eventually they will be "expended" and no longer fuel nuisance algaes (ie hair algae).

Is it truly the "rock" that is releasing the "nutrients" or is it microbial lifeforms on TOP of the rock?

I just think there is a lot of myth around dry rocks that can really be explained by having a sufficient level of herbivores in a tank or nutrient export methods that cause nuisance algae levels to eventually die down versus the dry rock being "expended" of its nutrients. For example, food (system input) is probably much more likely to fuel nuisance algae than the nutrients coming off of "Dry rock" ...

 

[Randy Holmes-Farley Verified Community Expert]

Calcium carbonate cannot ever bind or release nitrate (or ammonia) in any situation.

Calcium carbonate is very, very good at binding phosphate. That can be a sink or a source to the water, depending on whether the amount of phosphate in the water is higher or lower than the amount that would be in equilibrium with the amount on the rock.

Calcium carbonate can also be coated with organic matter, including dead organisms, that can decay and potentially become phosphate and nitrate in the water.