Roller coaster when dosing phosphate

[Steve1500]

I have been trying to get my phosphates up on my 70G reef. I have about 12 medium sized LPS and a few softies in the tank and 8 smaller fish. My nitrates are steady at 3-5 ppm without dosing, but I have to dose phosphate. About 2 weeks ago, I started dosing Neophos and the first time I dosed my phosphates showed at .12 ppm with just 5 ml. It was at 0.0 ppm. I dosed a few days later and found that it took up to 8ml to get to .03. So, i have been dosing btn 6 and 8 ml per day (split twice per day).

Last night i dosed 3 ml and decided to ck the ppm 10 minutes after dosing......0.0 ppm. Then I dosed another 3 and so on until I got to 30ml and it still read 0.0. (I changed the battery on the hanna checker).

According to the Neophos instructions I needed about 30 ml to get to .03ppm. Ok, so before I had been dosing much less and getting to .03 and now my phosphates don't even register...0.0ppm at 30 ml! Any ideas on why the roller coaster? Could my LR (60 lbs in the 70G tank) be fluctuating with absorption?

Thanks!

 

[Randy Holmes-Farley Verified Community Expert]

In such a situation, most of it will bind to rock and sand and so it is close to impossible to gauge the final concentration by calculation.

That said, it won’t fluctuate (except due to the amount in the water) and minor test error should also be considered.

 

[Steve1500]

Thanks Randy. Do you recommend I continue to dose at a lower rate say 8 ml per day or dose the recommended 30? If it’s in the rock then it’s still available to the coral right? I just don’t want to overdose.

Congratulations on your new job!

 

[PSXerholic]

Thanks Randy. Do you recommend I continue to dose at a lower rate say 8 ml per day or dose the recommended 30? If it’s in the rock then it’s still available to the coral right? I just don’t want to overdose.

Congratulations on your new job!

Hey Steve,
Your situation is quite normal when start dosing Phosphorus.
The trouble with Po4 dosing, and why it is such a painful job, is that as soon you start dosing PO4, the Rocks will sort of absorb quite some Po4 due to biological processes. At the same time, your bacteria will also find this as a food source. Means they also will populate to higher counts, and hence the consumption goes up again.
Bacteria I found personally will absorb the Po4 quite fast and fluctuating depending on carbon sources supplemented etc.
At a certain point of saturation of the rocks with Po4, they will stop absorbing most of the Po4 supplemented.
Finding the sweet spot takes a while.

My personal advice would be to reduce the Po4 consumption in your tank, by reducing the Po4 reduction methods, ideally to the point where it's not depleted and consumed that fast to these low levels. Things like reducing Chaeto, running the skimmer less effective, dose less carbs if any is dosed etc.
On the long run the Po4 management becomes very frustrating and difficult.
It's easier to establish a nutrient control household where Po4 is slowly consumed and more steady, so that only Nitrates have to be dosed if at all.
My personal philosophy is to somewhat set everything that Po4 is almost stable so only occasional corrections are necessary, and then focus only on dosing for Nitrates if required. Much easier ;-)

 

[Steve1500]

Hey Steve,
Your situation is quite normal when start dosing Phosphorus.
The trouble with Po4 dosing, and why it is such a painful job, is that as soon you start dosing PO4, the Rocks will sort of absorb quite some Po4 due to biological processes. At the same time, your bacteria will also find this as a food source. Means they also will populate to higher counts, and hence the consumption goes up again.
Bacteria I found personally will absorb the Po4 quite fast and fluctuating depending on carbon sources supplemented etc.
At a certain point of saturation of the rocks with Po4, they will stop absorbing most of the Po4 supplemented.
Finding the sweet spot takes a while.

My personal advice would be to reduce the Po4 consumption in your tank, by reducing the Po4 reduction methods, ideally to the point where it's not depleted and consumed that fast to these low levels. Things like reducing Chaeto, running the skimmer less effective, dose less carbs if any is dosed etc.
On the long run the Po4 management becomes very frustrating and difficult.
It's easier to establish a nutrient control household where Po4 is slowly consumed and more steady, so that only Nitrates have to be dosed if at all.
My personal philosophy is to somewhat set everything that Po4 is almost stable so only occasional corrections are necessary, and then focus only on dosing for Nitrates if required. Much easier ;-)

 

[Steve1500]

Thanks. Will heed your advice and try to be patient.... which is the hard part.

 

[chipmunkofdoom2]

Why are you dosing phosphates? How did you decide your tank was deficient on phosphates and needed supplementing?

 

[Steve1500]

Why are you dosing phosphates? How did you decide your tank was deficient on phosphates and needed supplementing?

My corals were not doing well and my N and P were zero. Using Hanna checker. Tried over feeding but no luck. Only tried over feeding for a week and gave up because I was not home enough.

 

[chipmunkofdoom2]

My corals were not doing well and my N and P were zero. Using Hanna checker. Tried over feeding but no luck. Only tried over feeding for a week and gave up because I was not home enough.

That sounds like a good reason. Many people get worried simply because their N and P read as zero and dose for no other reason than that, so I always ask

 

[Randy Holmes-Farley Verified Community Expert]

Thanks Randy. Do you recommend I continue to dose at a lower rate say 8 ml per day or dose the recommended 30? If it’s in the rock then it’s still available to the coral right? I just don’t want to overdose.

Congratulations on your new job!

It's not available to corals when bound to rock and sand, but on its way there it will be.

I actually doubt you'd detect a difference in terms of the corals from those two dosing amounts.

You can always stop dosing if levels rise too much. It's not like there a fixed amount the rock takes up then it suddenly spikes in the water when that reservoir is full. That reservoir on rock and sand increases a lot when the level in the water at equilibrium rises, and it shrinks as the levels fall.

 

[Steve1500]

It's not available to corals when bound to rock and sand, but on its way there it will be.

I actually doubt you'd detect a difference in terms of the corals from those two dosing amounts.

You can always stop dosing if levels rise too much. It's not like there a fixed amount the rock takes up then it suddenly spikes in the water when that reservoir is full. That reservoir on rock and sand increases a lot when the level in the water at equilibrium rises, and it shrinks as the levels fall.

Ok, if I am reading this right, I can continue to dose @ 20 or even 30 until the level gets too high?

 

[Randy Holmes-Farley Verified Community Expert]

Yes