Chronically low PO4

dragon99 · Oct 24, 2018

My tank is over 2 years old now and I still can't maintain a PO4 level over ~0.02 (Hanna ULR & ICP). Lately I've been dosing daily 5ml of Neophos which should be adding ~0.07ppm PO4. My last test came back 6ppb (Hanna ULR)

I believe some of the issue with my acropora growing well have been related to the low PO4 in the system related to the high NO3 (8-16ppm)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5441187/

Thoughts on what could cause such low PO4?

Red Sea 350 (78gal total system)
SG 1.026
Alk 9.5
Ca 425
Mg 1325
NO3 16ppm last test, prior months has been ~12ppm
Feeding multiple times daily with LRS Reef Frezny, occasionally reef roids, Hikari pellets
Dosing limewater via ATO w/ 30ml vinegar / gal RODI

saltyfilmfolks · Oct 24, 2018

You can likely stop the organic carbon dosing with the vinegar.
Like nopox , it Lowers no3 first, then Po4.
You probaly have low Po4 and a supercharged bio filter , plus livestock.

dragon99 · Oct 24, 2018

I did go about 4-5 months without it to see what difference it would make. It made none whatsoever. NO3/PO4 were pretty much the same during that time so I've gone back to using a little bit in my limewater. Helps me get more kalk dissolved and adds a food source

saltyfilmfolks · Oct 24, 2018

dragon99 said:
I did go about 4-5 months without it to see what difference it would make. It made none whatsoever. NO3/PO4 were pretty much the same during that time so I've gone back to using a little bit in my limewater. Helps me get more kalk dissolved and adds a food source

Oh, I know the pros of it.

Dunno. You may Just have to deal with a hungry tank. Comes down to feed more or dosing it.

dragon99 · Oct 24, 2018

saltyfilmfolks said:
Oh, I know the pros of it.

Dunno. You may Just have to deal with a hungry tank. Comes down to feed more or dosing it.

I think you are right, but I can't help but feel like something is off. Feeding more just increases my nitrate; I haven't seen more than a momentary increase in PO4. Dosing PO4 does seem to help, but that's probably all in my head.

saltyfilmfolks · Oct 24, 2018

dragon99 said:
I think you are right, but I can't help but feel like something is off. Feeding more just increases my nitrate; I haven't seen more than a momentary increase in PO4. Dosing PO4 does seem to help, but that's probably all in my head.

No, you’re correct. Po4 builds more slowly.
You’d have to feed more bones or shells to bump it.

It’s def possible it’s eating that much Po4.
It should be eating more no3 too. But again for builds back up faster.

jda · Oct 24, 2018

It is probably being bound up by the aragonite in your system... this is the momentary part where the water level rises and takes a day for the aragonite to bind it up and then the water levels test low again. If you keep adding the P, then the rock/sand would get more full and allow a higher concentration in the water - aragonite, along with GFO and Al Oxide, bind to "equilibrium*" with the water column. I would not sweat P of .02 - this is not a limiting factor in growth. If you are worried about a ratio, then bring the no3 down, if you can.

I do subscribe the anecdotes that high P and lower N can result in good things and that low P and high N do not... just anecdotes, though. Low of both, as long as they are not growth limiting, is OK too. .1n and .005p is not growth limiting, so have at least this much if you can.

*the binding is not linear and the more P that you add, the more that the rock will hold.

dragon99 · Oct 25, 2018

Bringing NO3 down is probably the best plan. I've generally tried to avoid worrying about it, but I could certainly cut back a little on the feeding.

Reefahholic · Oct 25, 2018

I'd back off on the carbon dosing first and then slowly supplement more PO4.

Randy Holmes-Farley · Oct 27, 2018

I'd just dose phosphate (the neophos is probably OK, but a DIY of known purity might have more assurance of quality) and don't really see any reason to worry "why you need more phosphate. The rock and sand is likely sucking up a lot of it. .