High Phosphate Levels


New member
Phosphates in my tank have always puzzled me. In my research there is a lot of opinions and controversy but I figured I'd throw this out here. Always ran about .15 to .2

After about a year months I bought a reactor to start trying GFO. Brought levels down to what in the hobby people seem to chase. Much to my surprise my corals were very unhappy with their new reality. I'm mostly torches, hammers and softies. They never really got used to their new levels which were between .05 and 1. Extension and color suffered.

After 2-3 months I decided to let the tank go. As of today I measured .33 (has com up slowly in the last month or so)"¦. Well my corals couldn't be happier. Extension is back. Color is better. They seem to be thriving.

I know not to chase numbers but how high is too high?


New member
That was an excellent lecture. Thank you for pointing it out!

I'm not going to sweat my PO4 numbers and not overly question where my tank and my corals take things as long as it seems to be working.


Premium Member
Not surprised and kudos for listening to your corals and not chasing nunmbers! What is not conveyed well in this hobby is corals are using forms of nitrogen and phosphorus we can't test for and the ratios of the various types are important, some are good some are bad. Unfortunately we tend to focus only on nitrates and phosphates that we can test for and invariable opinions form about what's "ideal" without considering the forms and ratios we cannot test for. Besides Richard Ross' video here's some more research you might find informative:

An Experimental Mesocosm for Longterm Studies of Reef Corals

Phosphate Deficiency:
Nutrient enrichment can increase the susceptibility of reef corals to bleaching:

Ultrastructural Biomarkers in Symbiotic Algae Reflect the Availability of Dissolved Inorganic Nutrients and Particulate Food to the Reef Coral Holobiont:

Phosphate deficiency promotes coral bleaching and is reflected by the ultrastructure of symbiotic dinoflagellates

Effects of phosphate on growth and skeletal density in the scleractinian coral Acropora muricata: A controlled experimental approach

High phosphate uptake requirements of the scleractinian coral Stylophora pistillata

Phosphorus metabolism of reef organisms with algal symbionts


Sponge symbionts and the marine P cycle

Phosphorus sequestration in the form of polyphosphate by microbial symbionts in marine sponges

Sugar enrichment provides evidence for a role of nitrogen fixation in coral bleaching

Elevated ammonium delays the impairment of the coral-dinoflagellate symbiosis during labile carbon pollution
(here's an argument for maintaining heavy fish loads if you're carbon dosing)

Excess labile carbon promotes the expression of virulence factors in coral reef bacterioplankton

Nitrogen cycling in hte coral holobiont

BActeria and Sponges