Creeping up Phosphate but bottom out Nitrate?

[Texastravis]

I feed nothing but rods food in my 120 gallon (small piece once per day), run a Clarisea roller, small skimmer, and Algae Turf Scrubber. Tank is approaching a year old, very few corals right now since struggling with algae.

In my eyes, my tank is very efficient at nutrient export, so much so that my nitrates occasionally bottom out at zero resulting in cyano. I have gotten past this by dosing nitrates up to 10ppm on occasion. The problem is, phosphate always seems to be above 0.05. When it gets up to 0.1, I drop a few drops of diluted LaCl to bring it back down which seems to happen weekly.

Whats up with this imbalance? Shouldn't Na and Ph nutrients be uptaken in equal amounts? Years ago in my old tanks, it seemed like Nitrate was the one that would creep up over time while phosphate stayed low as the limiting factor for refrugium growth. Am I missing something? Do corals take up phosphate more so than nitrate and so a lack of corals is the reason for needing LaCl to keep my phosphates low? Is Rod's food notoriously high in phosphate and low in nitrate and maybe I should switch food?

 

[djf91]

Following

 

[Dan_P]

I feed nothing but rods food in my 120 gallon (small piece once per day), run a Clarisea roller, small skimmer, and Algae Turf Scrubber. Tank is approaching a year old, very few corals right now since struggling with algae.

In my eyes, my tank is very efficient at nutrient export, so much so that my nitrates occasionally bottom out at zero resulting in cyano. I have gotten past this by dosing nitrates up to 10ppm on occasion. The problem is, phosphate always seems to be above 0.05. When it gets up to 0.1, I drop a few drops of diluted LaCl to bring it back down which seems to happen weekly.

Whats up with this imbalance? Shouldn't Na and Ph nutrients be uptaken in equal amounts? Years ago in my old tanks, it seemed like Nitrate was the one that would creep up over time while phosphate stayed low as the limiting factor for refrugium growth. Am I missing something? Do corals take up phosphate more so than nitrate and so a lack of corals is the reason for needing LaCl to keep my phosphates low? Is Rod's food notoriously high in phosphate and low in nitrate and maybe I should switch food?

Just curious, how old is your aquarium?

 

[Randy Holmes-Farley]

I feed nothing but rods food in my 120 gallon (small piece once per day), run a Clarisea roller, small skimmer, and Algae Turf Scrubber. Tank is approaching a year old, very few corals right now since struggling with algae.

In my eyes, my tank is very efficient at nutrient export, so much so that my nitrates occasionally bottom out at zero resulting in cyano. I have gotten past this by dosing nitrates up to 10ppm on occasion. The problem is, phosphate always seems to be above 0.05. When it gets up to 0.1, I drop a few drops of diluted LaCl to bring it back down which seems to happen weekly.

Whats up with this imbalance? Shouldn't Na and Ph nutrients be uptaken in equal amounts? Years ago in my old tanks, it seemed like Nitrate was the one that would creep up over time while phosphate stayed low as the limiting factor for refrugium growth. Am I missing something? Do corals take up phosphate more so than nitrate and so a lack of corals is the reason for needing LaCl to keep my phosphates low? Is Rod's food notoriously high in phosphate and low in nitrate and maybe I should switch food?

One possible explanation is that some of the nitrate is being consumed by denitrification, a bacterial process in sand and rock pores that reduces nitrate but not phosphate.

Another is ongoing release of phosphate from the rock.

 

[Texastravis]

One possible explanation is that some of the nitrate is being consumed by denitrification, a bacterial process in sand and rock pores that reduces nitrate but not phosphate.

Another is ongoing release of phosphate from the rock.

Tank is 1 year old. Randy, I did not think about denitrification. I have some sand but it is fairly shallow at about 1" but there might be some denitrification. I also bought one of those marinepure blocks for the sump just to see how it would do.

I was hoping not to have a phosphate issue with the rocks since I bleach cured for like 3 weeks outside before putting in the tank. Sand was all new out of the bag.

Is my problem a common problem? Currently, the problem is somewhat manageable with the addition of nitrate and occasional LaCl. I "think" that once my ATS gets in full swing and I actually get a handful of corals in there I can stop the LaCl altogether. I may never get to stop dosing nitrate though.

When I feed I dump into the MP40 and let is blow around the tank if that has any affect. Maybe I should turn the pumps off like some people do. I just figured letting it blow around would guarantee that all critters had a chance at food. I imagine though that uneaten food vs digested food/poop still results in similar Phosphate/Nitrate additions.