Nitrates and Phosphates - Water Change %

[disaster999]

FWIW, water changes are not the best way to deal with phosphate. Even a 100% change may end up only lowering the phosphate level slightly.

Why is that? Sure I get that rocks and other things in the tank can leach phosphate back, but I cant wrap my head around the statement that a 100% water change will only lower the level slightly

 

[BryanM]

Why is that? Sure I get that rocks and other things in the tank can leach phosphate back, but I cant wrap my head around the statement that a 100% water change will only lower the level slightly

Apparently “rock” can hold quite a lot of phosphate.

I can only guess that it lets out X amount over time, but still has plenty to give.

This is why it takes time to reduce, and even after a large water change people often end up with the same levels

 

[Dan_P]

Hi guys,

I have a 350L reef tank and am super high on nitrates and phosphates.

Here are my parameters:
Nitrates - 75+
Phosphates - 0.9
Alk - 15.2
Calcium - 520
Magnesium - 1230
Salinity - 1.026
pH - 8.3

I really need to reduce these numbers because I have a lot of algae and some of my coral aren’t so happy.

What % water change should I do and how frequently to avoid impacting my fish and coral negatively?

I’ve changed 15% each day for the last two days.

Should I keep doing 15% daily or what?

Any help would be appreciated!

Just finished reading the thread and want to repeat that if you are interested in lowering the nitrate concentration, you will need to know the actual concentration. Carbon dosing and water change will show no effect if the measurement cannot read above 75+. How do you know that the value hasn’t dropped from 100 to 80 ppm with your efforts? Also, it is unlikely that you are generating much nitrate everyday. More likely your system is just very good at accumulating it, meaning, the removal rate is slower than the generation rate.

By the way, the aquarium is a beauty.

 

[Randy Holmes-Farley Verified Community Expert]

Apparently “rock” can hold quite a lot of phosphate.

I can only guess that it lets out X amount over time, but still has plenty to give.

This is why it takes time to reduce, and even after a large water change people often end up with the same levels

Yes. Bare surfaces of calcium carbonate (rocks, sand, etc.) will bind phosphate, and the binding amount relates to the concentration of phosphate in the water (and the exposed surface area). Less binds at lower concentrations

If phosphate is 0.2 ppm in the water, there may be many times that amount bound to the rock surfaces.

If you do a 100% water change, the concentration in the water is suddenly 0.00 ppm. That causes an imbalance where there is now more on the rock and sand than is stable with that amount in the water, and some comes off. After a period of time (minutes/hours/days), the tank water might be back to 0.18 ppm (a made up number, but it correctly illustrates the situation and is not exaggerated), and there is somewhat less on the rock and sand.

You'd need to repeat that 100% change many times to get to, say, 0.03 ppm.

 

[taki123]

Just finished reading the thread and want to repeat that if you are interested in lowering the nitrate concentration, you will need to know the actual concentration. Carbon dosing and water change will show no effect if the measurement cannot read above 75+. How do you know that the value hasn’t dropped from 100 to 80 ppm with your efforts? Also, it is unlikely that you are generating much nitrate everyday. More likely your system is just very good at accumulating it, meaning, the removal rate is slower than the generation rate.

By the way, the aquarium is a beauty.

So I mixed 50% RODI to my Tankwater today then doubled my reading and my nitrates are 100.8ppm. Hanna would only show 75+ so before I didn’t know the exact number.

In regards to phosphates even after mixing RODI 50% Hanna still showed 0.9ppm. Which means it is over 1.8 lol

 

[SaltyCrew4u]

So I mixed 50% RODI to my Tankwater today then doubled my reading and my nitrates are 100.8ppm. Hanna would only show 75+ so before I didn’t know the exact number.

In regards to phosphates even after mixing RODI 50% Hanna still showed 0.9ppm. Which means it is over 1.8 lol

50% water change
Poly-Filter
Microbacter7

 

[SaltyCrew4u]

So I mixed 50% RODI to my Tankwater today then doubled my reading and my nitrates are 100.8ppm. Hanna would only show 75+ so before I didn’t know the exact number.

In regards to phosphates even after mixing RODI 50% Hanna still showed 0.9ppm. Which means it is over 1.8 lol

Also stop feeding pellets until you get your numbers down. Rinse your cubes before adding to tank. Do you add phyto?

 

[Randy Holmes-Farley Verified Community Expert]

50% water change
Poly-Filter
Microbacter7

What are you suggesting a polyfilter will do here?

 

[SaltyCrew4u]

What are you suggesting a polyfilter will do here?

To remove Phos. Works well for me and it removes anything else in my tank that I don't want.

 

[taki123]

Soemthing seems odd for me. With my Hanna when checking phosphates even when I put in 25% tank water and 75% RODI it still says 0.9ppm and flashes…does that mean my phosphates are like greater 3.6!? That sounds bizarre

 

[Randy Holmes-Farley Verified Community Expert]

To remove Phos. Works well for me and it removes anything else in my tank that I don't want.

A polyfilter cannot remove either phosphate or nitrate itself from seawater, and they do not literally claim that it does, although they are fast and loose with claims that might apply in freshwater and not clarifying if that is what they mean. There is too much competition from chloride and sulfate for any polymer to bind significant amounts of either phosphate or nitrate from seawater.

It will bind some organic matter, like GAC and purigen do, and may thereby have a reducing effect on nitrate and phosphate by removing organics before it can degrade.

 

[Randy Holmes-Farley Verified Community Expert]

Soemthing seems odd for me. With my Hanna when checking phosphates even when I put in 25% tank water and 75% RODI it still says 0.9ppm and flashes…does that mean my phosphates are like greater 3.6!? That sounds bizarre

Either that or a testing error of some sort.

 

[taki123]

Either that or a testing error of some sort.

So I’ve just performed a test with 10% tankwater and 90%. Finally got a reading of 0.46ppm.

Which means that 0.46x10 =4.6ppm is my accurate phosphate measurement lol.

Crazy stuff…most I’ve ever heard.

 

[taki123]

Could the way im testing by diluting RODI be giving an inaccurate reading? Or is that the right way to test. Any idea? @Randy Holmes-Farley

Maybe I should test by diluting with fresh sal water?

 

[Randy Holmes-Farley Verified Community Expert]

Could the way im testing by diluting RODI be giving an inaccurate reading? Or is that the right way to test. Any idea? @Randy Holmes-Farley

Maybe I should test by diluting with fresh sal water?

I think that is worth a try, but it may not matter. :)

 

[SaltyCrew4u]

A polyfilter cannot remove either phosphate or nitrate itself from seawater, and they do not literally claim that it does, although they are fast and loose with claims that might apply in freshwater and not clarifying if that is what they mean. There is too much competition from chloride and sulfate for any polymer to bind significant amounts of either phosphate or nitrate from seawater.

It will bind some organic matter, like GAC and purigen do, and may thereby have a reducing effect on nitrate and phosphate by removing organics before it can degrade.

I am only going off of personal experience. My aquarium is 36 gallons. I test twice a week using Hannah and Salifert. My phosphate went from .26 to .65 and that was my own doing. I added a poly-filter in my HOB Aquaclear 70, 10 ML of Microbacter7, and only did a 5 gallon water change, two days later my phos was at .14. I never said it would lower nitrates. I also didn't test nitrates. I kept my normal feeding schedule and rinsed my frozen food before broadcast feeding. I normally use ROWA Phos but this has been my go to with zero negative results. IMO it does reduce phosphate. AGAIN, add ROWA Phos, 50% water change and add Microbacter7. The ROWA will take a few days to start working.

 

[Randy Holmes-Farley Verified Community Expert]

I am only going off of personal experience. My aquarium is 36 gallons. I test twice a week using Hannah and Salifert. My phosphate went from .26 to .65 and that was my own doing. I added a poly-filter in my HOB Aquaclear 70, 10 ML of Microbacter7, and only did a 5 gallon water change, two days later my phos was at .14. I never said it would lower nitrates. I also didn't test nitrates. I kept my normal feeding schedule and rinsed my frozen food before broadcast feeding. I normally use ROWA Phos but this has been my go to with zero negative results. IMO it does reduce phosphate. AGAIN, add ROWA Phos, 50% water change and add Microbacter7. The ROWA will take a few days to start working.

I'm not doubting you observed what you did, I'm just stating that the explanation cannot include binding of inorganic phosphate with a polyfilter. This is not a case of your experience vs mine, but on understanding how polymers bind phosphate and where and how that happens. :)

I certainly agree that GFO (like Rowaphos) is a good way to reduce phosphate, though it can get expensive if one wants to lower phosphate a lot. The desorption of phosphate from calcium carbonate surfaces in the tank will make it look slow and somewhat ineffective, but it does work. It just may take large amounts over time.

 

[taki123]

Anyone here that uses Elimi Phos Rapid? What’s the max dosage I can dose at one time if my water volume is 350L. Existing Phosphates are 4.6.

Is the 3.5ml max I can dose?

 

[Randy Holmes-Farley Verified Community Expert]

Anyone here that uses Elimi Phos Rapid? What’s the max dosage I can dose at one time if my water volume is 350L. Existing Phosphates are 4.6.

Is the 3.5ml max I can dose?

I'd be very careful about "max dosage". Lowering phosphate fast has, IMO, led to more problems than high phosphate to begin with.

 

[taki123]

So some of my parameters are getting better now here’s the latest:

Alk - 11
Calcium - 480
Mag - 1230
Nitrate - 53
Phosphate - 2.2

My nitrates went from 101 down to 44 and then back up to 53ppm over last two days. Not sure why they are creeping up so quickly.

I’ve been carbon dosing for 2 months. I’m using a DIY NOPOX (60% Vinegar 40% Vodka) dosing 10ml on my 350L water.

Any idea what to do to keep my nitrates going down instead of up again? Should I change to Elimi NP rather than DIY carbon?