Carbon source for effective phosphate reduction

[rishma]

My tank has a heavy bio-load of corals and fish. For the last 3 years, I have been heavily using TM carbon dosing [Elimi NP (2X the recommended dose) and Reef Actif] combined with a Cheato refuge. My nitrates are around 0 even though I dose Amino Acids (TM). However, my phosphates are creeping up nowadays to above the limit of the Hanna ULR PO4 checker.
Now I will try to drain it with a GFO reactor. I do not worry about fast PO4 reduction as I assume that there is a lot of substrate-bound phosphate.

A couple thoughts…

Your nitrates being zero is connected to your phosphates drifting up. If you dose a nitrogen source like ammonium bicarbonate you can increase your nitrates and that will likely improve the phosphate reduction you achieve with carbon dosing.

Going slowly reducing phosphate in the water is recommended. I agree there is some bound in the substrate, but in the past I have stripped it quickly from the water with too much GFO and it was very stressful to the corals.

 

[Koty]

My nitrates are near zero most of the time. Dosing TM amino acids has a dual role: feeding the corals and supplying a nitrogen source. Thanks for the advice. I will monitor the phosphate levels. The GFP reactor has a rather slow flow through it. Also, an issue with TLF reactors is that they get clogged rather fast IME. So, they shut themselves off slowly...

 

[djkms]

03/25/2025 - 9PG per day
NO3 8.9
PO4 .11 (36ppb phosphorous)

increasing PG to 10ml per day
125ml ammonia bicarb = .5ppm NO3 daily



03/29/2025 - 10PG per day
NO3 8.4
PO4 .04 (12ppb phosphorous)

reducing PG to 7ml per day
125ml ammonia bicarb = .5ppm NO3 daily
75ml trisodium phosphate = .03 PO4 one time (PO4 dropped lower than I would like)

_________________________________________________________

Here is a summary so far:


03/10/2025
Propylene Glycol dosing day 1
5ml PG per day
NO3 8.3
PO4 .14ppm (47ppb Hanna ULR Phosphorous)



03/12/2025
5ml PG per day
NO3 6.7
PO4 .12 (38ppb phosphorous)



3/15/2025 - 5ml PG per day
NO3 8ppm
PO4 .16 (51ppb phosphorous)

Reduced ammonia dosing by 1/2 to 125ml = .5ppm NO3 daily
GFO reduced again to 59min off 1 min on (still need to take it offline)
increased PG to 8ml per day



03/18/2025 - 8ml PG per day
NO3 7.6
PO4 .12 (39ppb phosphorous)

reduced PG to 7ml per day (should be my break even, roughly)
125ml ammonia bicarb = .5ppm NO3 daily


3/22/2025 - 7ml PG per day
NO3 7.8ppm
PO4 .12 (40ppb phosphorous)

No GFO since last test
125ml ammonia bicarb = .5ppm NO3 daily

 

[Curiousbranching]

That’s an impressive result—congrats!

Have you noticed any changes in your corals? Is there any biofilm forming, similar to when using vinegar or NoPox?

 

[djkms]

That’s an impressive result—congrats!

Have you noticed any changes in your corals? Is there any biofilm forming, similar to when using vinegar or NoPox?

Thanks. Corals seem the same.

I do get a biofilm on the glass but it builds up every 2-3 days, with vinegar it was every day. I also had to change my filter socks almost every day with vinegar, now its roughly every 5 days.

 

[Koty]

I used vinegar dosing from the time I started it for a few years until I took the tank down. I only intend to use it on my new tank if nutrients exceeds
my new higher target levels. I’m hoping that macroalgae in the main tank and in a refugium, plus other consumers keeps it in reasonable control.

My view is that carbon dosing has other benefits beyond reducing nutrients. It supports and stabilizes a high level of coral microbiome. Although it's like an experiment without control, my corals (and fish and hair algae and bubble algae and now even colonial hydroids :confused:) have been doing great for close to 4 years now. I have about 40 different ones SPS, LPS. softies, Zoantides.

 

[djkms]

04/02/2025 - 7PG per day
NO3 10.1
PO4 .12 (38ppb phosphorous)

PO4 spiked higher than anticipated by .05
125ml ammonia bicarb = .5ppm NO3 daily



04/05/2025 - 7PG per day
NO3 11
PO4 .11 (37ppb phosphorous)

125ml ammonia bicarb = .5ppm NO3 daily

Now that I am over 10ppm nitrate I am removing ammonia dosing from the system to see the effect it has on PO4 reduction

 

[rsach]

04/02/2025 - 7PG per day
NO3 10.1
PO4 .12 (38ppb phosphorous)

PO4 spiked higher than anticipated by .05
125ml ammonia bicarb = .5ppm NO3 daily



04/05/2025 - 7PG per day
NO3 11
PO4 .11 (37ppb phosphorous)

125ml ammonia bicarb = .5ppm NO3 daily

Now that I am over 10ppm nitrate I am removing ammonia dosing from the system to see the effect it has on PO4 reduction

Sorry if I missed it, are you manually dosing PG?

 

[djkms]

Sorry if I missed it, are you manually dosing PG?

I dose it with a Neptune DOS between 9:30am-7:30pm directly into the display right above an mp60.

For context just how effective PG is, I feed 7 cubes of frozen 2 sheets of Nori and pellets through an auto feeder 3 times a day to 54 fish in a 600 gallon tank.

 

[rsach]

I dose it with a Neptune DOS between 9:30am-7:30pm directly into the display right above an mp60.

For context just how effective PG is, I feed 7 cubes of frozen 2 sheets of Nori and pellets through an auto feeder 3 times a day to 54 fish in a 600 gallon tank.

Thanks! Wow that's a lot of food..lol. I have been struggling with high Phosphates (0.6) and Nitrates (75) for quite a while. GFO has helped me lower it to 0.1 but then within a few weeks it creeps back up, I am also running a algae reactor. I'm scared to use phosphate E since I have tangs. I'll give PG a shot. Thanks for sharing your research.

 

[djkms]

Thanks! Wow that's a lot of food..lol. I have been struggling with high Phosphates (0.6) and Nitrates (75) for quite a while. GFO has helped me lower it to 0.1 but then within a few weeks it creeps back up, I am also running a algae reactor. I'm scared to use phosphate E since I have tangs. I'll give PG a shot. Thanks for sharing your research.

You're welcome. My only apprehension with dosing PG is the unknown of long term effects. Hopefully very little if none.

 

[djkms]

04/08/2025 - 7ml PG per day
NO3 10.7
PO4 .11 (37ppb phosphorous)

No ammonia dosing



04/12/2025 - 7ml PG per day
NO3 10.3
PO4 .13 (44ppb phosphorous)

No ammonia dosing


Observation: Interesting there was no difference in PO4 between Sunday and Tuesday however it did go up on the Saturday test by .02. Not a huge difference but its there. So far I don't see the ammonia dosing being a significant contributor to phosphate reduction but it's only been a week.

I currently feed 2 sheets of nori per day and my fish are destroying it too fast so I am going to increase my daily feeding of nori to 4 sheets. I am also increasing my PG dosing to 9ml per day to hopefully lower my PO4 a bit as I want to stay at or below .1. With my increased nori feeding and increased PG dosing I hope to accomplish this, or at the very least break even. We shall see how this weeks testing goes.

 

[Curiousbranching]

04/08/2025 - 7ml PG per day
NO3 10.7
PO4 .11 (37ppb phosphorous)

No ammonia dosing



04/12/2025 - 7ml PG per day
NO3 10.3
PO4 .13 (44ppb phosphorous)

No ammonia dosing


Observation: Interesting there was no difference in PO4 between Sunday and Tuesday however it did go up on the Saturday test by .02. Not a huge difference but its there. So far I don't see the ammonia dosing being a significant contributor to phosphate reduction but it's only been a week.

I currently feed 2 sheets of nori per day and my fish are destroying it too fast so I am going to increase my daily feeding of nori to 4 sheets. I am also increasing my PG dosing to 9ml per day to hopefully lower my PO4 a bit as I want to stay at or below .1. With my increased nori feeding and increased PG dosing I hope to accomplish this, or at the very least break even. We shall see how this weeks testing goes.

Or maybe the difference is just a matter of measurement error.

I’m wondering—if using PG doesn’t produce much bacterial biomass, then how are N and P being reduced? Could it be that another group of bacteria is responsible for this?

Overall, it looks like your method is really effective—congrats!

 

[djkms]

I wanted to give a quick update on the Propylene Glycol dosing as it is finally steady for the most part. PO4 testing at .1 every week

Currently dosing:

• 11ml PG per day
• 1.5ppm NO3 (dosed as ammonium bicarbonate) weekly to keep NO3 at 5ppm

Feeding:

• 6 cubes of frozen food daily
• 4 sheets of nori daily
• 1/3 sheet of nori every 3 days (sump)
• 1.2 grams of pellets daily

I wasn't really able to dial in the dosing until I got the plank auto feeder. I was using the Neptune AFS to feed and it was just too inconsistent. Now with the plank I really have the feeding dialed in.

 

[chema]

Hi, very interesting results. The take home message then is that by dosing PG you may control both nitrate (actually you have to dose it because the reduction rate is high) and phosphate without having to dose (voka/vinegar, for example) or use GFO. Am I right?

If so I'll give it a try. I used to control nitrate pretty well by using Bacto-Balance, but several months ago nitrate went up and now it is above 50 ppm. I dose the maximum amount (1 mL per 100). Phosphate is not bad. I have not changed the GFO in the filter for the last two months (therefore I'm pretty sure it is exhausted) and phosphate is around 0,19 ppm (60 ppb phosphorus).

 

[djkms]

Hi, very interesting results. The take home message then is that by dosing PG you may control both nitrate (actually you have to dose it because the reduction rate is high) and phosphate without having to dose (voka/vinegar, for example) or use GFO. Am I right?

If so I'll give it a try. I used to control nitrate pretty well by using Bacto-Balance, but several months ago nitrate went up and now it is above 50 ppm. I dose the maximum amount (1 mL per 100). Phosphate is not bad. I have not changed the GFO in the filter for the last two months (therefore I'm pretty sure it is exhausted) and phosphate is around 0,19 ppm (60 ppb phosphorus).

That has been my experience, yes. Although I don't know of any long term effects on the overall system and coral/fish health.

 

[Randy Holmes-Farley]

Thanks for the update. I’m not convinced pg does anything functionally different than other organics, but it’s good that it is working for you. :)

 

[chema]

Thanks for the update. I’m not convinced pg does anything functionally different than other organics, but it’s good that it is working for you. :)

I agree with you. I do not see why PG might have a substantially different effect from other organic carbon sources, but the results of the experiments dictate the conclusions and not the other way around.

 

[Randy Holmes-Farley]

I agree with you. I do not see why PG might have a substantially different effect from other organic carbon sources, but the results of the experiments dictate the conclusions and not the other way around.

Of course. But any organic will serve to help drive down P if one is simultaneously dosing N. :)