Phosphate won’t stabilize with dosing

[RickvDam]

Hello,
Since starting my tank 1,5 years ago I can’t get my Po4 and Nitrate stable for longer then a few weeks…

If I do nothing about the Po4, my nitrates are stable at 10 but my Po4 bottoms out in less then a day.
I tried dosing 0,02 daily, 0,04 daily and 0,06 daily. Every morning it’s back to 0 (Hanna checker).

Over the last weeks I’ve tried the 0,06 daily combined with a double dose of AB+, a double dose of Power Elixer, a double dose of AF Zoa food, a double dose of LPS pellets and a double dose of normal flakes and mysis (My corals are growing like crazy). I only change my filter floss once a week after a waterchange instead of every 2 days. My skimmer is on as it gives me a good stable pH, but it doesn’t skim much.

I finally managed to get my Po4 to the point is doesn’t bottom out but it swings like crazy, and now my Nitrates are bottoming out. I feed so much but whatever I do it doesn’t work.

I’d like to be able to stop the Po4 dosing, as I’m pretty sure that’s the reason my Nitrate is bottoming out (the more Po4 I dose, the more my Nitrate lowers). It’s a 15G with 2 clowns and a goby… Corals are all doing great, but the daily Hanna tests start adding up fast.

 

[Timfish]

There are other organisms using C, N and P besides corals. That increased PO4 dosing lowers nitrates suggests to me theres a lot growth causing the demand. In this scenario I wouldn't be worrying about keeping nitrates up, organisms in your system and diazatrophs in the coral microbiome can convert N2 into usable forms of nitrogen. I would focus more on keeping PO4 measurable to avoid creating a phospahte deficiency that would cause problems for corals. (FWIW, nitrates are corals least favorite form of N.)

 

[Randy Holmes-Farley]

A lot of the phosphate may be binding to rock and sand. You need to overcome that with dosing sodium phosphate.

 

[RickvDam]

A lot of the phosphate may be binding to rock and sand. You need to overcome that with dosing sodium phosphate.

I don’t clean my sand so you would think it would be filled by now… It’s been 1,5 year of daily dosing in a small tank… I don’t mind the dosing, but the way everytime atleast 1 of the 2 seems to bottom out when the other starts to stabilize drives me mad.

There are other organisms using C, N and P besides corals. That increased PO4 dosing lowers nitrates suggests to me theres a lot growth causing the demand. In this scenario I wouldn't be worrying about keeping nitrates up, organisms in your system and diazatrophs in the coral microbiome can convert N2 into usable forms of nitrogen. I would focus more on keeping PO4 measurable to avoid creating a phospahte deficiency that would cause problems for corals. (FWIW, nitrates are corals least favorite form of N.)

There is indeed a lot of growth in all my corals. If my nitrates drop to zero, what will happen in a day or 2, the dino’s are probably making a fast return… The phosphate dosing doesn’t bother me but one week it needs 0,1ml a day and the next week it needs 0,4ml a day to keep a steady level. I can’t just hook it up and let it go…

 

[PharmrJohn]

A lot of the phosphate may be binding to rock and sand. You need to overcome that with dosing sodium phosphate.

@Randy Holmes-Farley --- Two questions. Do Phosphates Absorb or Adsorb into/to live rock. Also, comparitively, what is the difference between phosphate salt addition with respect to the first question?

 

[Timfish]

@Randy Holmes-Farley --- Two questions. Do Phosphates Absorb or Adsorb into/to live rock. Also, comparitively, what is the difference between phosphate salt addition with respect to the first question?

That's anybody's guess. Biofilms can significantly alter the sorbtion properties of the surfaces they coat. They are also capable of sequestering significant amounts of phosphate. Cryptic sponges in your system can also have the capability of sequestering phosphate in crystaline form so can bind up significant amounts and what happens to that phosphate as they ebb and grow is up in the air. Personally I'd increase how much you're feeding your fish as fish poop has beneficial stuff besides urea and carbonates and phosphorus and a lot of the excess nitrogen will also be excreted as ammonia.

 

[Randy Holmes-Farley]

I don’t clean my sand so you would think it would be filled by now… It’s been 1,5 year of daily dosing in a small tank… I don’t mind the dosing, but the way everytime atleast 1 of the 2 seems to bottom out when the other starts to stabilize drives me mad.


There is indeed a lot of growth in all my corals. If my nitrates drop to zero, what will happen in a day or 2, the dino’s are probably making a fast return… The phosphate dosing doesn’t bother me but one week it needs 0,1ml a day and the next week it needs 0,4ml a day to keep a steady level. I can’t just hook it up and let it go…

It’s not a time issue, nor a “full” issue. Any time you try to raise phosphate, more binds. Any time you try to lower it, some releases. It’s like a buffer trying to hold the concentration where it is.

 

[Randy Holmes-Farley]

@Randy Holmes-Farley --- Two questions. Do Phosphates Absorb or Adsorb into/to live rock. Also, comparitively, what is the difference between phosphate salt addition with respect to the first question?

It binds to any exposed calcium carbonate. It likely does not bind to coralline.