0 PO4 ok if robust algae growth?

[rmurken]

Question: should I be doing something to run up my very, very low PO4 levels?

Situation:
My PO4 has bottomed out, testing 0 or 1ppb (.003ppm PO4) on the Hanna ULR. NO3 is about 7.5ppm. I don’t want dinos!

Everything is normal, and the tank is healthy. I run chaeto in my sump with a grow light on it at night. The chaeto grows great, and I have a healthy but manageable amount of algae that accumulates around the tank every other day or so. I don’t run GFO or Phosguard.

My gut is to just leave it, but appreciate thoughts.

Options for next steps if I need to do something is to reduce the photoperiod on the chaeto; turn off the skimmer part time; feed more (probably corals—fish already well-fed).

 

[sfin52]

If you are bottoming out nutrients cut the light back a little till you get the numbers you want.

 

[dragon99]

My experience is that 0 (or near) PO4 is bad for corals. Research also indicates it's a problem:

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

Enrichment of reef environments with dissolved inorganic nutrients is considered a major threat to the survival of corals living in symbiosis with dinoflagellates (Symbiodinium sp.). We argue, however, that the direct negative effects on the ...

www.ncbi.nlm.nih.gov

We exposed corals to imbalanced N : P ratios in long-term experiments and found that the undersupply of phosphate severely disturbed the symbiosis, indicated by the loss of coral biomass, malfunctioning of algal photosynthesis and bleaching of the corals.

https://digitalcommons.fiu.edu/cgi/viewcontent.cgi?article=3668&=&context=etd&=&sei-redir=1&referer=https%253A%252F%252Fscholar.google.de%252Fscholar%253Fhl%253Dde%2526as_sdt%253D0%25252C5%2526q%253Dshantz%252B%25252Bnitrogen%252Bphosphorus%252B%25252Binteractive%2526btnG%253D#search=%22shantz%20%2Bnitrogen%20phosphorus%20%2Binteractive%22

I show that P consistently increases coral growth rates while N has variable, often negative, effects on coral growth.

 

[rmurken]

My experience is that 0 (or near) PO4 is bad for corals. Research also indicates it's a problem:

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

Enrichment of reef environments with dissolved inorganic nutrients is considered a major threat to the survival of corals living in symbiosis with dinoflagellates (Symbiodinium sp.). We argue, however, that the direct negative effects on the ...

www.ncbi.nlm.nih.gov

We exposed corals to imbalanced N : P ratios in long-term experiments and found that the undersupply of phosphate severely disturbed the symbiosis, indicated by the loss of coral biomass, malfunctioning of algal photosynthesis and bleaching of the corals.

https://digitalcommons.fiu.edu/cgi/viewcontent.cgi?article=3668&=&context=etd&=&sei-redir=1&referer=https%253A%252F%252Fscholar.google.de%252Fscholar%253Fhl%253Dde%2526as_sdt%253D0%25252C5%2526q%253Dshantz%252B%25252Bnitrogen%252Bphosphorus%252B%25252Binteractive%2526btnG%253D#search=%22shantz%20%2Bnitrogen%20phosphorus%20%2Binteractive%22

I show that P consistently increases coral growth rates while N has variable, often negative, effects on coral growth.

Thanks. I have not had bleaching. Growth is slow, but that predates my PO4 issues. Like @sfin52 suggested, I am cutting my photoperiod on my chaeto to see if I can get PO4 to come up a bit that way.

 

[X-37B]

I would just feed more and it really depends on your alk level imo.
I run .02-.04 po4 and 2 no3 with an alk of 7-7.5.
Alk will read 0 on Hanna at times but I just feed more. Never had an issue.
I feed 3-4 times a day and have low algae growth and I have a sea hare that keeps it in check.
My coral growth and color is very good.
If you have algae you have po4 in your system.
What is your alk and is it stable.

 

[rmurken]

I would just feed more and it really depends on your alk level imo.
I run .02-.04 po4 and 2 no3 with an alk of 7-7.5.
Alk will read 0 on Hanna at times but I just feed more. Never had an issue.
I feed 3-4 times a day and have low algae growth and I have a sea hare that keeps it in check.
My coral growth and color is very good.
If you have algae you have po4 in your system.
What is your alk and is it stable.

Alk is stable around 8.5. Low alk demand. Maybe .5/day. Occasionally The demand stops for a day or two but always rights itself.

 

[X-37B]

Alk is stable around 8.5. Low alk demand. Maybe .5/day. Occasionally The demand stops for a day or two but always rights itself.

I lowered my alk from 8-8.5 to current 7-7.5 about 3-4 months ago.
It stays closer to 7.
I get better color with the same growth at lower alk levels in my tank with low nutrient levels.

 

[Backreefing]

Why do you run chaeto if you have low nutrients ( phosphate) why not take it offline for good . Or reduce chaeto light intensity or duration.

 

[Graffiti Spot]

If you have healthy living algae you do not have 0 po4. The algae is using the po4 so your test kit doesn’t see it. I wouldn’t worry about 0 po4 unless the algae starts to die or the tank is very clean.

 

[rmurken]

Why do you run chaeto if you have low nutrients ( phosphate) why not take it offline for good . Or reduce chaeto light intensity or duration.

I’ve had higher nutrients in the past, so I’m dropping the photoperiod on the chaeto until I start to get measurable PO4 or too much algae in the DT. I don’t carbon dose and am not trying to go ULN. As @Pedoconfuego suggests, I’ve got PO4 since I’m growing algae. I used to get decent PO4 readings with my Hanna ULR, and then they just dropped to 0. Not gonna chase numbers hard, but would be more comfortable with *some* reading.

Would prefer not to do away with Chaeto altogether since I like the pH support at night—no matter what I do, my tank’s pH runs a tad low unless I stay on it.